The switch may be worn,lack of track lube or sunroof motor is toast.

Make sure the sunroof is on it's track. If it's off by a fraction it won't
close. I had the same trouble with mine & brought it into MB as it is on
warranty.

Usually this will get worse soon, so fix it immediately...  In my
experience it's the cable that pushes and pulls the roof,  via a tube
that runs from the trunk of the car (where the motor is) to the middle
of the roof....

Removing the headliner piece from the sliding roof will let you get a
better look.

Mine had a frayed cable, which sounds like what you have also?