For reference there are three coin acceptor switch settings:

The positions for each switch are identified on the moulded plastic housing.

• Switch 1: set to MAX
• Switch 2: set to NO
• Switch 3: set to 25ms

Reject button can get stuck.   Take button out and smooth edges of metal hole.    Possibly bend top and bottom flanges around hole up to increase margins.   Wd-40 has been used successfully.

It’s reported that tightening bezel of coin acceptor can cause errors.   Apparently the metal plate can be warped and tightening it down makes it worse.   Loosen the bezel to minimize distortion.

If the above does not correct the problem, file the inner opening edges of metal sleeve.  Also, loosen the mounting screws of the Acceptor to a snug, but "Not" tight setting.