Key remote stopped working

[EuropaDrive]

Boxster base, no alarm system, key has 3 buttons. I had two working remotes until yesterday. One of them refuses to unlock the doors / frunk / trunk.

Both keys will still manually unlock and start the car. Windows go up or down if key is maintained in lock or unlock position from outside.

I replaced the battery (twice) as the first obvious step, although it was not that old and the red led still flashes when I press a button. It shows the same led flash pattern as the working remote, depending on which button I press.

I've tried a few things mentioned in other threads :

- reversed battery polarity to short / reset transmitter

- force-pressed the battery and press buttons

- ignition on for a few seconds, then press remote button

- disconnected car battery overnight

No luck.

Any chance that the remote has been "unlearned" ? Is there any way to check ?

Should I go to the dealer and see if they can reprogram it ?

Maybe it's flashing the led but transmitting garbage - or not transmitting ?

I still have the second working remote...but would prefer to have 2, if it's a relatively simple fix.