More information is needed before answering this.

You can open the rear hatch on a Xsara estate using the keyfob button or the “manual” release on the tailgate lift bar. I say manual release, it’s actually a switch which electrically operates the tailgate unlocking mechanism. The keyfob unlock is simply a wireless link to the same unlocking mechanism. Both functions are overseen by the onboard systems computer.

If the manual release works and the keyfob doesn’t, you have a problem with the keyfob or its programming. If the tailgate unlocks with the keyfob but not with the manual release there’s a fault with the tailgate switch, wiring or the function has been turned off by programming (being an estate, the hatch manual release can be de-activated so access to the cargo area is only possible with the keyfob).

I would advise against lubricating anything at this stage.