How to customize Edge's default 400 error message?

[#1]

We expose our API service at api.sandbox.amadeus.com.

Different sub-URLs of this domain go to different API proxies,but messages to the root service, or undefined proxies at https://api.sandbox.amadeus.com/ get an ugly error 400 with the following message

{"fault":{"faultstring":"Unable to identify proxy for host: default and url: \/","detail":{"errorcode":"messaging.adaptors.http.configuration.ApplicationNotFound"}}}

I would prefer to offer a more user friendly 404 message to the lost developer trying to find our API services. How can I customize this message to something that will point them in the right direction?