diff --git a/src/ORMP.sol b/src/ORMP.sol
index 15f4f47..117fdd5 100644
--- a/src/ORMP.sol
+++ b/src/ORMP.sol
@@ -37,8 +37,9 @@ contract ORMP is ReentrancyGuard, Channel {
     /// @param toChainId The Message destination chain id.
     /// @param to User application contract address which receive the message.
     /// @param encoded The calldata which encoded by ABI Encoding.
+    /// @param refund Return extra fee to refund address.
     /// @param params General extensibility for relayer to custom functionality.
-    function send(uint256 toChainId, address to, bytes calldata encoded, bytes calldata params)
+    function send(uint256 toChainId, address to, bytes calldata encoded, address refund, bytes calldata params)
         external
         payable
         sendNonReentrant
@@ -58,8 +59,8 @@ contract ORMP is ReentrancyGuard, Channel {
 
         //refund
         if (msg.value > relayerFee + oracleFee) {
-            uint256 refund = msg.value - (relayerFee + oracleFee);
-            (bool success,) = ua.call{value: refund}("");
+            uint256 refundFee = msg.value - (relayerFee + oracleFee);
+            (bool success,) = refund.call{value: refundFee}("");
             require(success, "!refund");
         }
 
diff --git a/src/interfaces/IORMP.sol b/src/interfaces/IORMP.sol
index 9cae3f1..a2b559a 100644
--- a/src/interfaces/IORMP.sol
+++ b/src/interfaces/IORMP.sol
@@ -25,9 +25,10 @@ interface IORMP {
     /// @param toChainId The Message destination chain id.
     /// @param to User application contract address which receive the message.
     /// @param encoded The calldata which encoded by ABI Encoding.
+    /// @param refund Return extra fee to refund address.
     /// @param params General extensibility for relayer to custom functionality.
     /// @return Return the hash of the message as message id.
-    function send(uint256 toChainId, address to, bytes calldata encoded, bytes calldata params)
+    function send(uint256 toChainId, address to, bytes calldata encoded, address refund, bytes calldata params)
         external
         payable
         returns (bytes32);
@@ -37,7 +38,7 @@ interface IORMP {
     //  @param to User application contract address which receive the message.
     /// @param encoded The calldata which encoded by ABI Encoding.
     /// @param params General extensibility for relayer to custom functionality.
-    function fee(uint256 toChainId, address, /*to*/ bytes calldata encoded, bytes calldata params)
+    function fee(uint256 toChainId, address to, bytes calldata encoded, bytes calldata params)
         external
         view
         returns (uint256);
diff --git a/test/ORMP.t.sol b/test/ORMP.t.sol
index c3451fd..5720e45 100644
--- a/test/ORMP.t.sol
+++ b/test/ORMP.t.sol
@@ -41,7 +41,7 @@ contract ORMPTest is Test, Verifier {
 
     function perform_send() public {
         uint256 f = ormp.fee(2, self, "", "");
-        ormp.send{value: f}(2, self, "", "");
+        ormp.send{value: f}(2, self, "", self, "");
         proof = Proof({blockNumber: block.number, messageIndex: ormp.messageCount() - 1, messageProof: ormp.prove()});
         vm.chainId(2);
     }
diff --git a/test/bench/ORMP.b.sol b/test/bench/ORMP.b.sol
index 03fab34..d61dd5b 100644
--- a/test/bench/ORMP.b.sol
+++ b/test/bench/ORMP.b.sol
@@ -80,6 +80,6 @@ contract ORMPBenchmarkTest is Test {
     function perform_send(uint256 fromChainId, uint256 toChainId, bytes calldata encoded) public {
         vm.createSelectFork(fromChainId.toChainName());
         uint256 f = ormp.fee(toChainId, self, encoded, abi.encode(uint256(0)));
-        ormp.send{value: f}(toChainId, self, encoded, abi.encode(uint256(0)));
+        ormp.send{value: f}(toChainId, self, encoded, self, abi.encode(uint256(0)));
     }
 }