Why did I receive the "Login failed" message when registering a tablet at a location?

Answer

If the Login failed message appears, it means the QR code you scanned has either expired (they are only valid for 24 hours) or you scanned a QR code that was not generated by the Server App:

Generate a new QR code in the Server App and then scan it.

For more information, see Registering a Tablet with a Location.