if i recall correctly, the side airbags are installed in the doors? If you've had the A-post connection separated at some point the airbag ECU will have detected an open circuit and will display the warning lamp. If that is the case then you'll need to have fault memory cleared.
This is a mk5 golf? Then there will be crash sensors inside the doors.
Not necessarily your dealer, any well equipped garage can do it for you for much much less.