Please make sure that the redirect URI that you have configured for the application registration matches exactly what you have configured for the app itself. (It can't have an extra space, slash, or anything else.) I'm not sure what type of application you are running but you can normally do a search through your code and check for references to the Redirect URI.
Please make sure that the application ID/Client IDs match both in the registration and in the application, as well as the tenant IDs.