Why isn't L3 working after installing a new joystick?

I'm repairing a Dualsense controller for someone that had some stick drift. I replaced the stick, but now for some reason when I connected it to my computer and test it in in a game, L3 doesn't respond. At first I thought there was a problem with the stick itself, but I checked it with my multimeter and the button is working, the controller just doesn't seem to do anything with the input. Does anybody know what might be going on?