When using Azure AD Premium’s Application Proxy feature, if you should receive an error that states “Status code: BadGateway” along with the line “The service detected a possible loop. Make sure that the internal URL doesn’t point to the external URL of any application.”
Example web page error:
The cause – when making a change to the internal URL, I had incidentally set the internal URL to use the external URL. The surprising thing is that App Proxy actually allowed me to save the changes!