Kwikset 910 having problems adding second lock to system I see the lock however states secure connection not established have pair within feet have rest controller and reinstalled all z wave devices at a loss GC2 being used.
To verify, the lock needs to remain within close proximity of the panel for a few minutes typically to ensure a successful pairing. If you bring it to the panel, perform the inclusion process, then quickly move it away the process may not finish.
It should be within about 6 feet.
Was this lock purchased as a used device? Depending on the original controller, other issues may be at play.