I've created an app for a client and we've now reached the app submission stage. I've submitted the app but it got rejected with the message of a functionality error which prevents the reviewer from installing or launching the app. I myself have not been able to recreate this error in any browser what so ever.
The error the reviewer encounters is simply "Request origin could not be verified" as an inline message instead of the app.
I encountered another error myself a few weeks ago and a forum post from the community lead me to change my App URL to: https://domain.com/auth/inline which fixed my error.