diff --git a/.travis.yml b/.travis.yml
index 741f61d1..05401da9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,6 +5,7 @@ php:
   - 7.0
   - 7.1
   - 7.2
+  - 7.3
 
 # This triggers builds to run on the new TravisCI infrastructure.
 # See: http://docs.travis-ci.com/user/workers/container-based-infrastructure/
diff --git a/README.md b/README.md
index e3b693c3..6bf31f30 100644
--- a/README.md
+++ b/README.md
@@ -111,15 +111,16 @@ $data = $response->getData();
 
 $data['paymentProfile']['customerProfileId'];
 $data['paymentProfile']['customerPaymentProfileId'];
-//Now you can use these 2 fields to reference this customer and this payment profile for later use with 
-//the rest of the CIM driver features as usual.
+
+// Now you can use these 2 fields to reference this customer and this payment profile for later use with 
+// the rest of the CIM driver features as usual.
 ```
 
 ## DPM and SIM Signatures
 
 DPM and SIM used to sign their requests with the `transactionKey` using the mdh HMAC algorithm.
 From early 2019, this algorithm is being removed completely.
-Instead, the SHA-512 HMAC algorithm is used to sign the DPM and SIM requsts,
+Instead, the SHA-512 HMAC algorithm is used to sign the DPM and SIM requests,
 and to validate the received  notifications.
 
 To start using the SHA-512 signing, set your `signatureKey` in the gateway:
diff --git a/src/Message/DPMAuthorizeRequest.php b/src/Message/DPMAuthorizeRequest.php
index 8bcf1829..8fd631d9 100644
--- a/src/Message/DPMAuthorizeRequest.php
+++ b/src/Message/DPMAuthorizeRequest.php
@@ -6,6 +6,7 @@
  * Authorize.Net DPM Authorize Request.
  * Takes the data that will be used to create the direct-post form.
  */
+
 class DPMAuthorizeRequest extends SIMAuthorizeRequest
 {
     protected $action = 'AUTH_ONLY';
diff --git a/src/Message/DPMCompleteRequest.php b/src/Message/DPMCompleteRequest.php
index 54cf5774..28a75dcf 100644
--- a/src/Message/DPMCompleteRequest.php
+++ b/src/Message/DPMCompleteRequest.php
@@ -5,7 +5,7 @@
 /**
  * Authorize.Net DPM Complete Authorize Request
  */
-class DPMCompleteRequest extends SIMCompleteAuthorizeRequest
+class DPMCompleteRequest extends SIMCompleteRequest
 {
     public function sendData($data)
     {
diff --git a/src/Message/DPMCompleteResponse.php b/src/Message/DPMCompleteResponse.php
index 92975509..26df385f 100644
--- a/src/Message/DPMCompleteResponse.php
+++ b/src/Message/DPMCompleteResponse.php
@@ -5,6 +5,6 @@
 /**
  * SIM and DPM both have identical needs when handling the notify request.
  */
-class DPMCompleteResponse extends SIMCompleteAuthorizeResponse
+class DPMCompleteResponse extends SIMCompleteResponse
 {
 }
diff --git a/src/Message/SIMAbstractRequest.php b/src/Message/SIMAbstractRequest.php
index 7224cb9b..05668230 100644
--- a/src/Message/SIMAbstractRequest.php
+++ b/src/Message/SIMAbstractRequest.php
@@ -2,11 +2,12 @@
 
 namespace Omnipay\AuthorizeNet\Message;
 
-use Omnipay\Common\Message\AbstractRequest;
-
 /**
  * Authorize.Net SIM Abstract Request
  */
+
+use Omnipay\Common\Message\AbstractRequest;
+
 abstract class SIMAbstractRequest extends AbstractRequest
 {
     /**
diff --git a/src/Message/SIMAuthorizeRequest.php b/src/Message/SIMAuthorizeRequest.php
index 4c35f219..db1fb7df 100644
--- a/src/Message/SIMAuthorizeRequest.php
+++ b/src/Message/SIMAuthorizeRequest.php
@@ -54,7 +54,8 @@ public function getData()
         }
 
         $data = array_merge($data, $this->getBillingData());
-        $data['x_fp_hash'] = $this->getHash($data);
+
+        $data['x_fp_hash'] = $this->createHash($data);
 
         return $data;
     }
@@ -64,10 +65,11 @@ public function getData()
      * modified en-route.
      * It uses the TransactionKey, which is a shared secret between the merchant
      * and Authorize.Net The sequence and timestamp provide additional salt.
+     *
      * @param $data
      * @return string
      */
-    public function getHash($data)
+    public function createHash($data)
     {
         $fingerprint = implode(
             '^',
@@ -77,7 +79,7 @@ public function getHash($data)
                 $data['x_fp_timestamp'],
                 $data['x_amount']
             )
-        ).'^';
+        ) . '^';
 
         // If x_currency_code is specified, then it must follow the final trailing carat.
 
diff --git a/src/Message/SIMAuthorizeResponse.php b/src/Message/SIMAuthorizeResponse.php
index 0daad075..e0972a53 100644
--- a/src/Message/SIMAuthorizeResponse.php
+++ b/src/Message/SIMAuthorizeResponse.php
@@ -44,4 +44,11 @@ public function getRedirectData()
     {
         return $this->getData();
     }
+
+    public function getTransactionId()
+    {
+        return isset($this->data[SIMAbstractRequest::TRANSACTION_ID_PARAM])
+            ? $this->data[SIMAbstractRequest::TRANSACTION_ID_PARAM]
+            : null;
+    }
 }
diff --git a/src/Message/SIMCompleteAuthorizeRequest.php b/src/Message/SIMCompleteAuthorizeRequest.php
deleted file mode 100644
index 26d3f7f0..00000000
--- a/src/Message/SIMCompleteAuthorizeRequest.php
+++ /dev/null
@@ -1,86 +0,0 @@
-<?php
-
-namespace Omnipay\AuthorizeNet\Message;
-
-use Omnipay\Common\Exception\InvalidRequestException;
-
-/**
- * Authorize.Net SIM Complete Authorize Request
- */
-class SIMCompleteAuthorizeRequest extends SIMAbstractRequest
-{
-    /**
-     * Get the transaction ID passed in through the custom field.
-     * This is used to look up the transaction in storage.
-     */
-    public function getTransactionId()
-    {
-        return $this->httpRequest->request->get(static::TRANSACTION_ID_PARAM);
-    }
-
-    public function getData()
-    {
-        // The hash sent in the callback from the Authorize.Net gateway.
-        $hash_posted = strtolower($this->httpRequest->request->get('x_MD5_Hash'));
-
-        // The transaction reference generated by the Authorize.Net gateway and sent in the callback.
-        $posted_transaction_reference = $this->httpRequest->request->get('x_trans_id');
-
-        // The amount that the callback has authorized.
-        $posted_amount = $this->httpRequest->request->get('x_amount');
-
-        // Calculate the hash locally, using the shared "hash secret" and login ID.
-        $hash_calculated = $this->getHash($posted_transaction_reference, $posted_amount);
-
-        if ($hash_posted !== $hash_calculated) {
-            // If the hash is incorrect, then we can't trust the source nor anything sent.
-            // Throwing exceptions here is probably a bad idea. We are trying to get the data,
-            // and if it is invalid, then we need to be able to log that data for analysis.
-            // Except we can't, baceuse the exception means we can't get to the data.
-            // For now, this is consistent with other OmniPay gateway drivers.
-
-            throw new InvalidRequestException('Incorrect hash');
-        }
-
-        // The hashes have passed, but the amount should also be validated against the
-        // amount in the stored and retrieved transaction. If the application has the
-        // ability to retrieve the transaction (using the transaction_id sent as a custom
-        // form field, or perhaps in an otherwise unused field such as x_invoice_id.
-
-        $amount = $this->getAmount();
-
-        if (isset($amount) && $amount != $posted_amount) {
-            // The amounts don't match. Someone may have been playing with the
-            // transaction references.
-
-            throw new InvalidRequestException('Incorrect amount');
-        }
-
-        return $this->httpRequest->request->all();
-    }
-
-    /**
-     * CHECKME: should this be the transactionReference in the hash, not the transactionId?
-     * The transaction reference and the amount are both sent by the remote gateway (x_trans_id
-     * and x_amount) and it is those that should be checked against.
-     * @param $transaction_reference
-     * @param $amount
-     * @return string
-     */
-    public function getHash($transaction_reference, $amount)
-    {
-        $key = array(
-            $this->getHashSecret(),
-            $this->getApiLoginId(),
-            $transaction_reference,
-            $amount,
-         );
-
-        return md5(implode('', $key));
-    }
-
-    public function sendData($data)
-    {
-        return $this->response = new SIMCompleteAuthorizeResponse($this, $data);
-    }
-}
diff --git a/src/Message/SIMCompleteRequest.php b/src/Message/SIMCompleteRequest.php
new file mode 100644
index 00000000..72427692
--- /dev/null
+++ b/src/Message/SIMCompleteRequest.php
@@ -0,0 +1,158 @@
+<?php
+
+namespace Omnipay\AuthorizeNet\Message;
+
+use Omnipay\Common\Exception\InvalidRequestException;
+
+/**
+ * Authorize.Net SIM Complete Authorize Request
+ */
+class SIMCompleteRequest extends SIMAbstractRequest
+{
+    /**
+     * Get the transaction ID passed in through the custom field.
+     * This is used to look up the transaction in storage.
+     */
+    public function getTransactionId()
+    {
+        return $this->httpRequest->request->get(static::TRANSACTION_ID_PARAM);
+    }
+
+    public function getData()
+    {
+        // The hash sent in the callback from the Authorize.Net gateway.
+        $hashPosted = $this->getPostedHash();
+
+        // Calculate the hash locally, using the shared "hash secret" and login ID.
+        $hashCalculated = $this->getHash();
+
+        if ($hashPosted !== $hashCalculated) {
+            // If the hash is incorrect, then we can't trust the source nor anything sent.
+            // Throwing exceptions here is probably a bad idea. We are trying to get the data,
+            // and if it is invalid, then we need to be able to log that data for analysis.
+            // Except we can't, baceuse the exception means we can't get to the data.
+            // For now, this is consistent with other OmniPay gateway drivers.
+
+            throw new InvalidRequestException('Incorrect hash');
+        }
+
+        // The hashes have passed, but the amount should also be validated against the
+        // amount in the stored and retrieved transaction. If the application has the
+        // ability to retrieve the transaction (using the transaction_id sent as a custom
+        // form field, or perhaps in an otherwise unused field such as x_invoice_id.
+
+        $amount = $this->getAmount();
+        $postedAmount = $this->httpRequest->request->get('x_amount');
+
+        if (isset($amount) && $amount != $postedAmount) {
+            // The amounts don't match. Someone may have been playing with the
+            // transaction references.
+
+            throw new InvalidRequestException('Incorrect amount');
+        }
+
+        return $this->httpRequest->request->all();
+    }
+
+    /**
+     * @return string
+     */
+    public function getHash()
+    {
+        if ($this->getSignatureKey()) {
+            return $this->getSha512Hash();
+        } else {
+            return $this->getMd5Hash();
+        }
+    }
+
+    /**
+     * Generate md5 hash.
+     *
+     * @param $transaction_reference
+     * @param $amount
+     * @return string
+     */
+    public function getMd5Hash()
+    {
+        $transactionReference = $this->httpRequest->request->get('x_trans_id');
+        $amount = $this->httpRequest->request->get('x_amount');
+
+        $key = array(
+            $this->getHashSecret(),
+            $this->getApiLoginId(),
+            $transactionReference,
+            $amount,
+        );
+
+        return md5(implode('', $key));
+    }
+
+    /**
+     * Generate sha512 hash.
+     * Required fields are provided in Table 18 in
+     * https://www.authorize.net/content/dam/authorize/documents/SIM_guide.pdf#page=73
+     *
+     * @return string hash generated from server request transformed to upper case
+     */
+    public function getSha512Hash()
+    {
+        $signatureKey = $this->getSignatureKey();
+        $request = $this->httpRequest->request;
+
+        $hashData = '^' . implode('^', [
+            $request->get('x_trans_id'),
+            $request->get('x_test_request'),
+            $request->get('x_response_code'),
+            $request->get('x_auth_code'),
+            $request->get('x_cvv2_resp_code'),
+            $request->get('x_cavv_response'),
+            $request->get('x_avs_code'),
+            $request->get('x_method'),
+            $request->get('x_account_number'),
+            $request->get('x_amount'),
+            $request->get('x_company'),
+            $request->get('x_first_name'),
+            $request->get('x_last_name'),
+            $request->get('x_address'),
+            $request->get('x_city'),
+            $request->get('x_state'),
+            $request->get('x_zip'),
+            $request->get('x_country'),
+            $request->get('x_phone'),
+            $request->get('x_fax'),
+            $request->get('x_email'),
+            $request->get('x_ship_to_company'),
+            $request->get('x_ship_to_first_name'),
+            $request->get('x_ship_to_last_name'),
+            $request->get('x_ship_to_address'),
+            $request->get('x_ship_to_city'),
+            $request->get('x_ship_to_state'),
+            $request->get('x_ship_to_zip'),
+            $request->get('x_ship_to_country'),
+            $request->get('x_invoice_num'),
+        ]) . '^';
+        $hash = hash_hmac('sha512', $hashData, hex2bin($signatureKey));
+
+        return strtoupper($hash);
+    }
+
+    /**
+     * Get posted hash from the callback from the Authorize.Net gateway.
+     *
+     * @return string|null
+     */
+    public function getPostedHash()
+    {
+        if ($signatureKey = $this->getSignatureKey()) {
+            return strtoupper($this->httpRequest->request->get('x_SHA2_Hash'));
+        }
+
+        return strtolower($this->httpRequest->request->get('x_MD5_Hash'));
+    }
+
+    public function sendData($data)
+    {
+        return $this->response = new SIMCompleteResponse($this, $data);
+    }
+}
diff --git a/src/Message/SIMCompleteAuthorizeResponse.php b/src/Message/SIMCompleteResponse.php
similarity index 97%
rename from src/Message/SIMCompleteAuthorizeResponse.php
rename to src/Message/SIMCompleteResponse.php
index b7270d34..ed05befa 100644
--- a/src/Message/SIMCompleteAuthorizeResponse.php
+++ b/src/Message/SIMCompleteResponse.php
@@ -2,14 +2,15 @@
 
 namespace Omnipay\AuthorizeNet\Message;
 
+/**
+ * Authorize.Net SIM Complete Authorize Response
+ */
+
 use Omnipay\Common\Message\AbstractResponse;
 use Omnipay\Common\Message\RedirectResponseInterface;
 use Symfony\Component\HttpFoundation\Response as HttpResponse;
 
-/**
- * Authorize.Net SIM Complete Authorize Response
- */
-class SIMCompleteAuthorizeResponse extends AbstractResponse implements RedirectResponseInterface
+class SIMCompleteResponse extends AbstractResponse implements RedirectResponseInterface
 {
     // Response codes returned by Authorize.Net
 
diff --git a/src/SIMGateway.php b/src/SIMGateway.php
index ae8a143b..b8566a56 100644
--- a/src/SIMGateway.php
+++ b/src/SIMGateway.php
@@ -60,7 +60,7 @@ public function authorize(array $parameters = array())
 
     public function completeAuthorize(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\AuthorizeNet\Message\SIMCompleteAuthorizeRequest', $parameters);
+        return $this->createRequest('\Omnipay\AuthorizeNet\Message\SIMCompleteRequest', $parameters);
     }
 
     public function capture(array $parameters = array())
diff --git a/tests/Message/DPMAuthorizeRequestTest.php b/tests/Message/DPMAuthorizeRequestTest.php
index 54521bd1..9b018ea7 100644
--- a/tests/Message/DPMAuthorizeRequestTest.php
+++ b/tests/Message/DPMAuthorizeRequestTest.php
@@ -81,7 +81,7 @@ public function testGetHash()
 
         $expected = hash_hmac('md5', 'user^a^b^c^', 'key');
 
-        $this->assertSame($expected, $this->request->getHash($data));
+        $this->assertSame($expected, $this->request->createHash($data));
     }
 
     public function testSend()
diff --git a/tests/Message/DPMCompleteRequestTest.php b/tests/Message/DPMCompleteRequestTest.php
index c22202b5..28684d41 100644
--- a/tests/Message/DPMCompleteRequestTest.php
+++ b/tests/Message/DPMCompleteRequestTest.php
@@ -8,7 +8,7 @@
 
 use Omnipay\Tests\TestCase;
 
-class DPMCompleteAuthorizeRequestTest extends TestCase
+class DPMCompleteRequestTest extends TestCase
 {
     public function setUp()
     {
@@ -25,14 +25,69 @@ public function testGetDataInvalid()
         $this->request->getData();
     }
 
-    public function testGetHash()
+    public function testGetMd5Hash()
     {
-        $this->assertSame(md5(''), $this->request->getHash('', ''));
+        $this->assertSame(md5(''), $this->request->getHash());
 
         $this->request->setHashSecret('hashsec');
         $this->request->setApiLoginId('apilogin');
 
-        $this->assertSame(md5('hashsec' . 'apilogin' . 'trnid' . '10.00'), $this->request->getHash('trnid', '10.00'));
+        $this->getHttpRequest()->request->replace(
+            array(
+                'x_trans_id' => 'trnid',
+                'x_amount' => '10.00',
+            )
+        );
+
+        $this->assertSame(
+            md5('hashsec' . 'apilogin' . 'trnid' . '10.00'),
+            $this->request->getHash()
+        );
+    }
+
+    public function testGetSha512Hash()
+    {
+        $this->request->setSignatureKey('48D2C629E4AE7CA3C4E6CD7223DA');
+
+        $this->getHttpRequest()->request->replace(
+            array(
+                'x_trans_id' => 'trn123456',
+                'x_test_request' => 'xxx',
+                'x_response_code' => 'xxx',
+                'x_auth_code' => 'xxx',
+                'x_cvv2_resp_code' => 'xxx',
+                'x_cavv_response' => 'xxx',
+                'x_avs_code' => 'xxx',
+                'x_method' => 'xxx',
+                'x_account_number' => 'xxx',
+                'x_amount' => '10.99',
+                'x_company' => 'xxx',
+                'x_first_name' => 'xxx',
+                'x_last_name' => 'xxx',
+                'x_address' => 'xxx',
+                'x_city' => 'xxx',
+                'x_state' => 'xxx',
+                'x_zip' => 'xxx',
+                'x_country' => 'xxx',
+                'x_phone' => 'xxx',
+                'x_fax' => 'xxx',
+                'x_email' => 'xxx',
+                'x_ship_to_company' => 'xxx',
+                'x_ship_to_first_name' => 'xxx',
+                'x_ship_to_last_name' => 'xxx',
+                'x_ship_to_address' => 'xxx',
+                'x_ship_to_city' => 'xxx',
+                'x_ship_to_state' => 'xxx',
+                'x_ship_to_zip' => 'xxx',
+                'x_ship_to_country' => 'xxx',
+                'x_invoice_num' => 'xxx',
+            )
+        );
+
+        $this->assertSame(
+            'F9A0DE7A9AC83E0B8043CD7CBD804ED41FE6BFDDB2C10C486DB4E3C4F3E7163237837A5CD6AEE1FAFF03BAD076DF287F7E81E17ED38752999D1AA6249ECC1613',
+            $this->request->getHash()
+        );
     }
 
     public function testSend()
diff --git a/tests/Message/DPMPurchaseRequestTest.php b/tests/Message/DPMPurchaseRequestTest.php
index cceaf94f..07c6f458 100644
--- a/tests/Message/DPMPurchaseRequestTest.php
+++ b/tests/Message/DPMPurchaseRequestTest.php
@@ -70,7 +70,7 @@ public function testGetHash()
 
         $expected = hash_hmac('md5', 'user^a^b^c^', 'key');
 
-        $this->assertSame($expected, $this->request->getHash($data));
+        $this->assertSame($expected, $this->request->createHash($data));
     }
 
     public function testSend()
diff --git a/tests/Message/SIMAuthorizeRequestTest.php b/tests/Message/SIMAuthorizeRequestTest.php
index 497f9ecd..7cc56474 100644
--- a/tests/Message/SIMAuthorizeRequestTest.php
+++ b/tests/Message/SIMAuthorizeRequestTest.php
@@ -52,7 +52,7 @@ public function testGetHash()
 
         $expected = hash_hmac('md5', 'user^a^b^c^', 'key');
 
-        $this->assertSame($expected, $this->request->getHash($data));
+        $this->assertSame($expected, $this->request->createHash($data));
     }
 
     public function testSend()
diff --git a/tests/Message/SIMCompleteAuthorizeRequestTest.php b/tests/Message/SIMCompleteAuthorizeRequestTest.php
deleted file mode 100644
index 840e7424..00000000
--- a/tests/Message/SIMCompleteAuthorizeRequestTest.php
+++ /dev/null
@@ -1,66 +0,0 @@
-<?php
-
-namespace Omnipay\AuthorizeNet\Message;
-
-use Omnipay\Tests\TestCase;
-
-class SIMCompleteAuthorizeRequestTest extends TestCase
-{
-    public function setUp()
-    {
-        $this->request = new SIMCompleteAuthorizeRequest($this->getHttpClient(), $this->getHttpRequest());
-    }
-
-    /**
-     * @expectedException \Omnipay\Common\Exception\InvalidRequestException
-     * @expectedExceptionMessage Incorrect hash
-     */
-    public function testGetDataInvalid()
-    {
-        $this->getHttpRequest()->request->replace(array('x_MD5_Hash' => 'invalid'));
-        $this->request->getData();
-    }
-
-    public function testGetHash()
-    {
-        $this->assertSame(md5(''), $this->request->getHash('', ''));
-
-        $this->request->setHashSecret('hashsec');
-        $this->request->setApiLoginId('apilogin');
-
-        $this->assertSame(md5('hashsec' . 'apilogin' . 'trnref ' . '10.00'), $this->request->getHash('trnref ', '10.00'));
-    }
-
-    public function testSend()
-    {
-        $posted_trans_id = '12345'; // transactionReference in POST.
-        $posted_amount = '10.00'; // amount authothorised in POST.
-
-        $this->getHttpRequest()->request->replace(
-            array(
-                'x_response_code' => '1',
-                'x_trans_id' => $posted_trans_id,
-                'x_amount' => $posted_amount,
-                'x_MD5_Hash' => md5('shhh' . 'user' . $posted_trans_id . $posted_amount),
-                'omnipay_transaction_id' => '99',
-            )
-        );
-        $this->request->setApiLoginId('user');
-        $this->request->setHashSecret('shhh');
-        $this->request->setAmount('10.00');
-        $this->request->setReturnUrl('http://example.com/');
-
-        // Issue #22 Transaction ID in request is picked up from custom field.
-        $this->assertSame('99', $this->request->getTransactionId());
-
-        $response = $this->request->send();
-
-        $this->assertTrue($response->isSuccessful());
-        $this->assertSame($posted_trans_id, $response->getTransactionReference());
-        $this->assertSame(true, $response->isRedirect());
-        // CHECKME: does it matter what letter case the method is?
-        $this->assertSame('GET', $response->getRedirectMethod());
-        $this->assertSame('http://example.com/', $response->getRedirectUrl());
-        $this->assertNull($response->getMessage());
-    }
-}
diff --git a/tests/Message/SIMCompleteRequestTest.php b/tests/Message/SIMCompleteRequestTest.php
new file mode 100644
index 00000000..594a710c
--- /dev/null
+++ b/tests/Message/SIMCompleteRequestTest.php
@@ -0,0 +1,124 @@
+<?php
+
+namespace Omnipay\AuthorizeNet\Message;
+
+use Omnipay\Tests\TestCase;
+
+class SIMCompleteRequestTest extends TestCase
+{
+    public function setUp()
+    {
+        $this->request = new SIMCompleteRequest(
+            $this->getHttpClient(),
+            $this->getHttpRequest()
+        );
+    }
+
+    /**
+     * @expectedException \Omnipay\Common\Exception\InvalidRequestException
+     * @expectedExceptionMessage Incorrect hash
+     */
+    public function testGetDataInvalid()
+    {
+        $this->getHttpRequest()->request->replace(array('x_MD5_Hash' => 'invalid'));
+        $this->request->getData();
+    }
+
+    public function testGetMd5Hash()
+    {
+        $this->assertSame(md5(''), $this->request->getHash());
+
+        $this->request->setHashSecret('hashsec');
+        $this->request->setApiLoginId('apilogin');
+
+        $this->getHttpRequest()->request->replace(
+            array(
+                'x_trans_id' => 'trnref',
+                'x_amount' => '10.00',
+            )
+        );
+
+        $this->assertSame(
+            md5('hashsec' . 'apilogin' . 'trnref' . '10.00'),
+            $this->request->getHash()
+        );
+    }
+
+    public function testGetSha512Hash()
+    {
+        $this->request->setSignatureKey('48D2C629E4AE7CA3C4E6CD7223DA');
+
+        $this->getHttpRequest()->request->replace(
+            array(
+                'x_trans_id' => 'trn123456',
+                'x_test_request' => 'xxx',
+                'x_response_code' => 'xxx',
+                'x_auth_code' => 'xxx',
+                'x_cvv2_resp_code' => 'xxx',
+                'x_cavv_response' => 'xxx',
+                'x_avs_code' => 'xxx',
+                'x_method' => 'xxx',
+                'x_account_number' => 'xxx',
+                'x_amount' => '10.99',
+                'x_company' => 'xxx',
+                'x_first_name' => 'xxx',
+                'x_last_name' => 'xxx',
+                'x_address' => 'xxx',
+                'x_city' => 'xxx',
+                'x_state' => 'xxx',
+                'x_zip' => 'xxx',
+                'x_country' => 'xxx',
+                'x_phone' => 'xxx',
+                'x_fax' => 'xxx',
+                'x_email' => 'xxx',
+                'x_ship_to_company' => 'xxx',
+                'x_ship_to_first_name' => 'xxx',
+                'x_ship_to_last_name' => 'xxx',
+                'x_ship_to_address' => 'xxx',
+                'x_ship_to_city' => 'xxx',
+                'x_ship_to_state' => 'xxx',
+                'x_ship_to_zip' => 'xxx',
+                'x_ship_to_country' => 'xxx',
+                'x_invoice_num' => 'xxx',
+            )
+        );
+
+        $this->assertSame(
+            'F9A0DE7A9AC83E0B8043CD7CBD804ED41FE6BFDDB2C10C486DB4E3C4F3E7163237837A5CD6AEE1FAFF03BAD076DF287F7E81E17ED38752999D1AA6249ECC1613',
+            $this->request->getHash()
+        );
+    }
+
+    public function testSend()
+    {
+        $posted_trans_id = '12345'; // transactionReference in POST.
+        $posted_amount = '10.00'; // amount authothorised in POST.
+
+        $this->getHttpRequest()->request->replace(
+            array(
+                'x_response_code' => '1',
+                'x_trans_id' => $posted_trans_id,
+                'x_amount' => $posted_amount,
+                'x_MD5_Hash' => md5('shhh' . 'user' . $posted_trans_id . $posted_amount),
+                'omnipay_transaction_id' => '99',
+            )
+        );
+        $this->request->setApiLoginId('user');
+        $this->request->setHashSecret('shhh');
+        $this->request->setAmount('10.00');
+        $this->request->setReturnUrl('http://example.com/');
+
+        // Issue #22 Transaction ID in request is picked up from custom field.
+        $this->assertSame('99', $this->request->getTransactionId());
+
+        $response = $this->request->send();
+
+        $this->assertTrue($response->isSuccessful());
+        $this->assertSame($posted_trans_id, $response->getTransactionReference());
+        $this->assertSame(true, $response->isRedirect());
+        // CHECKME: does it matter what letter case the method is?
+        $this->assertSame('GET', $response->getRedirectMethod());
+        $this->assertSame('http://example.com/', $response->getRedirectUrl());
+        $this->assertNull($response->getMessage());
+    }
+}
diff --git a/tests/Message/SIMCompleteAuthorizeResponseTest.php b/tests/Message/SIMCompleteResponseTest.php
similarity index 58%
rename from tests/Message/SIMCompleteAuthorizeResponseTest.php
rename to tests/Message/SIMCompleteResponseTest.php
index 35732ec5..152047a0 100644
--- a/tests/Message/SIMCompleteAuthorizeResponseTest.php
+++ b/tests/Message/SIMCompleteResponseTest.php
@@ -4,11 +4,14 @@
 
 use Omnipay\Tests\TestCase;
 
-class SIMCompleteAuthorizeResponseTest extends TestCase
+class SIMCompleteResponseTest extends TestCase
 {
     public function testSuccess()
     {
-        $response = new SIMCompleteAuthorizeResponse($this->getMockRequest(), array('x_response_code' => '1', 'x_trans_id' => '12345'));
+        $response = new SIMCompleteResponse(
+            $this->getMockRequest(),
+            array('x_response_code' => '1', 'x_trans_id' => '12345')
+        );
 
         $this->assertTrue($response->isSuccessful());
         $this->assertSame('12345', $response->getTransactionReference());
@@ -17,7 +20,10 @@ public function testSuccess()
 
     public function testFailure()
     {
-        $response = new SIMCompleteAuthorizeResponse($this->getMockRequest(), array('x_response_code' => '0', 'x_response_reason_text' => 'Declined'));
+        $response = new SIMCompleteResponse(
+            $this->getMockRequest(),
+            array('x_response_code' => '0', 'x_response_reason_text' => 'Declined')
+        );
 
         $this->assertFalse($response->isSuccessful());
         $this->assertNull($response->getTransactionReference());