Side sliding door locking problem with Central locking

[Newt]

Hi , I’m having a slight problem with the side sliding door on my Sprinter 314 2018 plate . It doesn’t unlock with the fob , yet if I go inside the rear and open it , I can then lock the door and unlock it for a few goes to the point it seems fine then it stops working and I’m forced to open it from the inside again . Does anyone have any suggestions, I’ve read on here to clean the pins and contact plate which I’ve not tried , any thoughts please would be appreciated. Thanks