diff --git a/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerError.scala b/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerError.scala
index 5a27032b75..4c7208fda0 100644
--- a/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerError.scala
+++ b/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerError.scala
@@ -1,6 +1,6 @@
 package org.hyperledger.identus.didcomm.controller
 
-import org.hyperledger.identus.mercury.model.DidId
+import org.hyperledger.identus.mercury.model.{DidId, PIURI}
 import org.hyperledger.identus.shared.models.{Failure, KeyId, StatusCode}
 
 sealed trait DIDCommControllerError extends Failure {
@@ -39,4 +39,10 @@ object DIDCommControllerError {
     override def userFacingMessage: String =
       s"The Peer DID does not contain the required key: DID=${did.value}, keyId=${keyId.value}"
   }
+
+  final case class UnsupportedPIURI(piuri: PIURI) extends DIDCommControllerError {
+    override def statusCode: StatusCode = StatusCode.UnprocessableContent
+    override def userFacingMessage: String =
+      s"The Protocol Identifier URI (URI) found in the DIDComm message is not supported: PIURI=$piuri"
+  }
 }
diff --git a/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerImpl.scala b/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerImpl.scala
index b910ace0f4..b13d522e03 100644
--- a/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerImpl.scala
+++ b/cloud-agent/service/server/src/main/scala/org/hyperledger/identus/didcomm/controller/DIDCommControllerImpl.scala
@@ -184,8 +184,8 @@ class DIDCommControllerImpl(
   /*
    * Unknown Message
    */
-  private val handleUnknownMessage: PartialFunction[Message, UIO[String]] = { case _ =>
-    ZIO.succeed("Unknown Message Type")
+  private val handleUnknownMessage: PartialFunction[Message, IO[UnsupportedPIURI, String]] = { case msg =>
+    ZIO.fail(UnsupportedPIURI(msg.piuri))
   }
 }