Seeing Error message: 401 Unauthorized: Access is denied due to invalid credentials. On my mobile app.

This is generally due to the auth cookie on the device. The "fix" in this case is from within the app on the phone where you are seeing the 401 page. Select the navigation "hamburger" (three horizontal lines) and then select sign out from the bottom of that navigation. The app should present you with the Username and Password filed to log in again. After doing this the app authorization should be restored.