Sliding door won't lock.

[B.different]

Hi all hope you can help me with a customer's van. It's a t6.1 that has had the drivers side repaired. Since the repair the passenger side loading door won't lock. Any idea what could have failed. It's been to vw who was useless. Apparently when you clear the fault codes you have to replace the lock good one vw thats a new one on me. Any help would be appreciated before I order the full gubbins.