The system couldn't connect to the application. Either the authentication details are incorrect or there is a temporary system or network problem. Verify the authentication details and test the connection again."

I have a web server running locally to handle the request, however no request is received at all. I've set up the custom application correctly, and am able to use it as an identity provider to grant access to my custom application running at the above url. Is there some pre-requisite to setting up account lifecycle management for a custom application that I'm missing? Why does the test connection request not even make it to the custom application server? I've tried both Basic Authentication and OAuth Bearer Token, but neither work.