Hi Team
just joined the site as I see loads of users involved in helping others.

I have a 2015 Mazda 6 Wagon (2.5L 4 Cyl).
Got the car 7 months or so ago from a second hand dealer, the car came with two key fobs.
Recently (first time since had car) I swapped key fobs as the main one needed a battery and until I could get a battery thought I would switch to the backup.
But for whatever reason the spare key fob simply does not work with the door button to lock/unlock (request switch I believe it is called).
It will unlock the car and start the car no issue, but unlock/lock only via buttons on the key fob itself.

Any known simple reason for this or does it require a dealer fix?
I tried and tried to search existing forums, found some guides but these appeared to be for older model cars.
I attach an image of my key fob (both same and interestingly same look as my Wifes older 2008 Atenza).

Thanks a bunch
Stretch