Epson pos printer receipt not validating

Epson TM-H5000II used for many places, receipts,restaurant, car park tickets, sometimes it doesn't want to receive the ticket. due to a few reason as below -Ribbon is loose or something it uses the ERC31 Ribbon -The sensor is covered or faulty so just make sure to clean it make sure no dust is on it. The sensor is shown in the video it's a small little square.Make sure it's not dirty or covered in dust or something.