diff --git a/README.md b/README.md
index 29a639c..cc0c714 100644
--- a/README.md
+++ b/README.md
@@ -60,4 +60,28 @@ $ anchor build
 To run the tests
 ```bash
 $ anchor test
-```
\ No newline at end of file
+```
+
+# Relevant Account and Addresses
+
+The Gateway program derive a PDA (Program Derived Address)
+with seeds `b"meta"` and canonical bump. 
+This PDA account/address actually holds the SOL
+balance of the Gateway program. For SPL tokens, 
+the PDA derived ATA (Associated Token Account) is
+used to hold the SPL token balance.
+
+The PDA account itself is a data account that holds
+Gateway program state, namely the following data types
+```rust
+pub struct Pda {
+    nonce: u64,            // ensure that each signature can only be used once
+    tss_address: [u8; 20], // 20 bytes address format of ethereum
+}
+```
+The `nonce` is incremented on each successful withdraw transaction,
+and it's used to prevent replay of signed ECDSA messages. 
+The `tss_address` is the TSS address of ZetaChain (20Bytes,
+Ethereum style). 
+
+The `initialize` instruction sets nonce to 0. 
\ No newline at end of file
diff --git a/tests/protocol-contracts-solana.ts b/tests/protocol-contracts-solana.ts
index 2a7351d..8fdf677 100644
--- a/tests/protocol-contracts-solana.ts
+++ b/tests/protocol-contracts-solana.ts
@@ -23,11 +23,16 @@ describe("some tests", () => {
     let pda_ata: spl.Account;
 
     it("Initializes the program", async () => {
-        let transaction = new anchor.web3.Transaction();
-        console.log("wallet address", wallet.publicKey.toString());
-        // Add your test here.
-        transaction.add(await gatewayProgram.methods.initialize().instruction());
-        await anchor.web3.sendAndConfirmTransaction(anchor.getProvider().connection, transaction, [wallet]);
+        await gatewayProgram.methods.initialize().rpc();
+
+        // repeated initialization should fail
+        try {
+            await gatewayProgram.methods.initialize().rpc();
+            throw new Error("Expected error not thrown"); // This line will make the test fail if no error is thrown
+        } catch (err) {
+            expect(err).to.be.not.null;
+            // console.log("Error message: ", err.message)
+        }
     });
 
     it("Mint a SPL USDC token", async () => {