Hi, I'm a newbie Multipla owner.
So far so good, but the front passenger seat belt seems a bit shorter than the driver's side belt. Is there a longer belt option? Any ideas how to make/replace it longer?

How about something like these if you only want a couple of inches :-
https://www.ebay.co.uk/itm/153521588260

OR

This if you want a bit longer (36cm / 14 inches) :-
https://www.ebay.co.uk/itm/264220602238

Both only £3 -to- £4 quidish .... Should hopefully fit your needs