Door not locking

There's an electric lock actuator unit on the rear piller. No idea how you get to it but someone may know how.
When you press your remote alarm button to lock the doors remotely do you hear anything click or clock in the passenger door?

Complete pig of a job if it it’s the solenoid blown, often do after a few years and years.

Easiest to remove whole door lock mechanism and replace - easy to find solenoids, then make sure you can reuse the connectors required to actuate, reassemble and reseal door lock mechanism into door aperture.

Likely need to rewire different coloured wires from aftermarket solenoids as well. Did both my doors earlier this year, pain the ass job, but easy enough.

You may get lucky and find the door light courtesy switch isn’t being actuated by the door, which may cause the issue as the relay thinks the doors open. Often the push button style switches corrode as they’re exposed to quite a lot of crud, or there are little rubber pads used to make sure they’re compressed sufficiently, which go missing.. Fitted in the side skirt/scuttle of the body. I’d check your interior light operates on and off with doors opening first, if not I’d start there before tackling solenoid replacement.