To customize the message returned to end users a catch all policy can be configured
1. Launch policy manager
2. Publish a Web API
[9.1] Tasks Menu -> Service and APIs -> Publish Web API
[9.0 and under] Tasks -> Publish Web API
3. Enter the resolution path as an asterisk (*). This will catch all calls at the root of the Gateway.
4. Click finish
5. You can now write a policy to suite your needs. Common uses are using a 'Return Template Response' assertion with an HTTP error code and status message such as: