diff --git a/src/Message/ServerCompleteAuthorizeRequest.php b/src/Message/ServerCompleteAuthorizeRequest.php
index 118ddfb..799a323 100644
--- a/src/Message/ServerCompleteAuthorizeRequest.php
+++ b/src/Message/ServerCompleteAuthorizeRequest.php
@@ -53,7 +53,12 @@ public function getSignature()
             $this->httpRequest->request->get('DeclineCode', '').
             $this->httpRequest->request->get('ExpiryDate', '').
             $this->httpRequest->request->get('FraudResponse', '').
-            $this->httpRequest->request->get('BankAuthCode', '');
+            $this->httpRequest->request->get('BankAuthCode', '').
+            // New for protocol v4.00
+            // Described in the docs here: https://developer.elavon.com/products/opayo-server/v1/notification-of-transaction-result
+            $this->httpRequest->request->get('ACSTransID', '').
+            $this->httpRequest->request->get('DSTransID', '').
+            $this->httpRequest->request->get('SchemeTraceID', '');
 
         return md5($signature_string);
     }
diff --git a/tests/ServerGatewayTest.php b/tests/ServerGatewayTest.php
index 468eedb..c762e4d 100644
--- a/tests/ServerGatewayTest.php
+++ b/tests/ServerGatewayTest.php
@@ -120,9 +120,14 @@ public function testCompleteAuthorizeSuccess()
                 'DeclineCode' => '00',
                 'ExpiryDate' => '0722',
                 'BankAuthCode' => '999777',
+                // New fields for protocol v4.0
+                'ACSTransID' => 'abcuuid',
+                'DSTransID' => '123uuid',
+                'SchemeTraceID' => 'V123',
                 'VPSSignature' => md5(
                     '{F955C22E-F67B-4DA3-8EA3-6DAC68FA59D2}'
                     . '438791' . 'OK' . 'bexamplecJEUPDN1N7Edefghijklm' . '00' . '0722' . '999777'
+                    . 'abcuuid' . '123uuid' . 'V123'
                 ),
             )
         );