Air bag light constantly on

You need a good obd scanner. If you don’t have that it needs to go to a mechanic

If i had to take a guess not knowing the make or model, I'd say clock spring is gone.

But get a diagnostic done, an amazon OBD may just show you airbag light is on.

Make and model please?

Has this fault occurred within your ownership? Or did you buy the car with the light on?

…. delete.

is there wiring under the seats? Get your hands in and have a play around trying to tighten connections. Recently had an issue and that solved it (entirely different car).

might be unrelated, but if the guy doing nct was tall and slammed seat back could have done something. Move seat forward as far as you can, put torch in your phone and see if there is any connections that you give a hand squeeze on when accessing from behind.

In my older BMWs there was a little "bypass piece" you could buy and plug in to the seat belt tensioner/occupancy

I done that too a fair few years ago when I had my e39. I also fixed my parents airbag light by joining two wires together under their drivers seat as the factory connection must have stopped connecting the two wires together. I didn't figure that out myself I googled the car and problem and it was a common problem but it was an easy fit. I also unbolted the seat and swung it back over the back seats to give more working room and get a better look.

Did you have to get fault cleared at a garage after?

BMW obviously charging for new part and whatever labour time they pull out of their ass.

Why would you even bother. Of course they are going to be multiples of the price of an independent dealer and a 2nd hand part.

The Lesson is stay away from them where possible. They don't even expect to sell parts for 20 year old cars.