Okay, the transmitters in the fobs are working, as is the receiver in the car, or you’d get no response at all from the remote. I’m going to assume that you can unlock the doors with the central locking system from inside the car without the key fob, or you would have mentioned otherwise. That leaves only one variable: the unlock button on the key fob itself. Times two, of course.

Normally, when I have a bad key fob, I pick up a generic remote at the spare parts store and use the remaining working remote to program it. (No surprise, these units are far cheaper than the dealer-sourced ones.) Follow the directions on the replacement fob, since they’re too complicated to list here.

Unfortunately, in your case, both remotes aren’t working properly, which makes reprogramming a new one tough. I predict the issue is bad electrical contacts inside the fob. Pry or unscrew it open. Find the small microswitches soldered to the printed circuit board and hose them down with contact cleaner. Try the lock button again. If that works, immediately acquire a generic fob and use the now-functioning OEM fob to program it, because odds are it will fail again sooner or later.