diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1b017e0..9db567d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## 3.1.2
+
+* add content type header to the http client default headers list
+
 ## 3.1.1
 
 * small naming update for data removal endpoints
diff --git a/package-lock.json b/package-lock.json
index de04106..905778a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "postmark",
-  "version": "3.1.1",
+  "version": "3.1.2",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "postmark",
-      "version": "3.1.1",
+      "version": "3.1.2",
       "license": "MIT",
       "dependencies": {
         "axios": "^0.25.0"
diff --git a/package.json b/package.json
index 2b08a0a..b0c3326 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
     "sending",
     "transactional"
   ],
-  "version": "3.1.1",
+  "version": "3.1.2",
   "author": "Igor Balos",
   "contributors": [
     "Igor Balos",
diff --git a/src/client/BaseClient.ts b/src/client/BaseClient.ts
index 84d8509..d98b490 100644
--- a/src/client/BaseClient.ts
+++ b/src/client/BaseClient.ts
@@ -110,6 +110,7 @@ export default abstract class BaseClient {
         return {
             [this.authHeader]: this.token,
             "Accept": "application/json",
+            "Content-Type": "application/json",
             "User-Agent": `Postmark.JS - ${this.clientVersion}`,
         };
     }