Hi, SNM, I fit roller shutters, and we'd normally pack off to miss the handle, either with timber ie, 3"x2", or steel angle or box section. Paint your packers to match the shutter and they look fine.
If the belt mechanism is running, but the door isn't moving, then it sounds like the manual release handle may have been pulled and not re-engaged. Press the green button on the trolley, then operate the door. It should engage on its way past.