[WeslyMKE]

Thank you for your reply. The “shop” tells me that there is a problem with the airbag system by itself and that I should order a new replacement kit for the brain of the airbags, with a cost at around 150€.
Is there any chance that the airbag system is corrupted, leading to the seat light also to flashing?

I don't have the link handy, but if you do some searching about the airbag light with head unit replacement you will see that this happens when the indicator is disconnected and the car turned on or to "accessory." I am pretty sure there is a quick way to reset it.

Actually, I found the post (original was deleted but a response further down has a procedure):

"sorry to ask but i removed my head unit to install music for my car and fortunately i did turn ignition on... how can a i reset the airbag problem on dash if i have push to start ignition?"

Follow these simple steps:​

1) Put the vehicle in Accessory Mode (the airbag light should stay solid for a few seconds)​

2) Once the airbag light turns off, press the button to shut your car off immediately​

3) Do this process 3-4 times and it will reset the light to work again​