A BT/A Keypad is not absolutely necessary.
If the GM/A 8.1 is operated together with the KNX, the GM/A be programmed and operated once using the WebUI. However, this requires structured parameterization on the KNX. An operating point should be provided on the KNX so that, for example, an unintentional setting can be canceled. Please also keep alternating service personnel in mind.