PO or Evri should ignore it as they have a contract to accept any oversized or weight items if sold by Simple Delivery on Ebay.  I have had this a few times and another way round it is to get a wider box and package an item 61cm long sideways in the box this will usually bring it down to a 61cm length. Its just another stupid thing Ebay haven't thought through properly in the hope of extracting more money from you.