On my Smartcode 909/910, the Lock button does not lock the door.
No user codes are programmed.
If there are no codes in the lock, the lock button will not lock the door. This is indicated by the keypad flashing red three times with three beeps. Program at least one user code and test the Lock button again.
The door handing process was not executed.
Perform the door handing process, following the instructions inside the installation guide.
The battery is too low to lock the door.
This is indicated by the keypad flashing red three times with three beeps. Remove the batteries and replace with a fresh set.
The latch is installed upside down.
The clutch is disengaged.
The mounting plate is placing tension on the torque blade.
For Smarcode 909 see page 8 here.
For Smartcode 910 see page 8 here.