Trying to pair tx134 remotes with a 202u receiver

I am trying to pair new tx134 remotes to a 202u receiver being used to open and close a driveway gate. When I go to press the program 1 or 2 button, the red led light comes on but does not stay on for programming. So the red light goes on when I press the button but does not stay on in order to program one of the buttons on the tx134 remove (a,b,c, or d). have not been able to find any information online about what that would mean or what to do next. the old remotes are working fine but need more remotes.

Hi,
For 202U v5, you will need to keep PRG button pressed during the programming procedure.
Please see video below for more details.

Thanks.