Hiace door lock failure

Could be a defective door switch or a problem with the wiring harness leading to it. Have you checked the cable and plug connection of the component?

Where exactly would I find that cable and plug connection? Is it something easily accessible?

It's usually located within the door, near the latch mechanism. If you're not comfortable disassembling the door panel, it's best to get it checked by a workshop.

Thanks for the help! I took it to a local mechanic, and it turned out to be a defective cable and plug connection, just as you suspected. Repair cost me 95€. Sorted now!