So, you got an error with a code AADSTS50011? It’s just Azure AD’s authentication acting up because of invalid reply address! here’s a bunch of different reasons that lead to this error. This post describes the variant where the URL’s case sensitivity differns from what’s configured. For me, the most typical scenario where I run into this error is accessing the app from SharePoint.
So, you’re getting an error somewhat like this:
AADSTS50011: The reply address <...> does not match the reply addresses configured for the application: '<guid>'. More details: Reply address did not match because of case sensitivity.
This is another variation of the good old “AADSTS50011: The reply address does not match the reply addresses configured“-error.
I recently encountered this new version of the error. Normally, you don’t get any extra details – the “More details:” -section will just say “not available” or some such. But I guess a lot of people have been struggling with the case-sensitivity of the URLs (I wonder who thought that was a good idea?), and Microsoft has opted to provide this, slightly improved version of the classical reply-url error.