Airbag or belt failure

Friends I have the new case c3 1.6 triptonic gear car. The vehicle beeps while on the move and briefly displays an airbag or belt malfunction on the display, and then goes out, sometimes it does it sometimes and sometimes it does not. When I took the car to the workshop, they looked at the sockets under the seats and made a test drive, but at that time they couldn't find anything because it didn't fail and said there might be a contact in place. What do you think I should do? Have you ever had such a situation?

There is a possibility that there may be no contact depending on what you do once in a while, but the problem may be solved by the authorized service inspection.

They say that it does not record the fault, it appears from the computer when it burns.