When the API Gateway audit log contains “Message was not processed: Undefined (-1)”, there may be some issue with the URL being used to route the request to the backend application or service. For example, let’s say requests are being routed to http://example.com:12345/enterprise/sample.

• Protocol: The protocol may need to be HTTP or HTTPS. 
• Hostname: Using nslookup, ensure the host name can be resolved to an IP address. Also ensure that the application or service exists on the server that the host name resolves to.
• Port: The port will need to be open on the target server - this usually means checking the web or application server the request is being routed to.
• Context root: The context root, such as /enterprise/sample, does not always need to match the context root of the service. The developer should be able to provide you with the valid context root.

If there is an issue with the URL being used to route the requests to the backend application or service, events will not be written to the application server logs, such as SystemOut.log (WebSphere), catalina.log (Tomcat), or mule_ee.log (Mule), as the API Gateway is not able to establish a connection to the application server.