Push the smart button momentarily (do not hold it), push one of the
transmitter buttons within 30 seconds. Push the smart button again
momentarily & push the other transmitter button within 30 seconds.

Holding the smart button (as some directions say to do) for more than
10 seconds (smart button LED goes out) erases the memory. If you have
to erase the memory to get the second transmitter to work, the
transmitters are not compatible. One is rolling code & one isn't. It's
possible for a transmitter to lose its rolling code capability & if it
does it's non-repairable & needs to be replaced.

Doordoc
www.DoorsAndOpeners.com