For collection items now , the buyers receive a 6 digit QR code which they must bring to the seller, as this is the only method a seller has to mark the item as collected. The numbers are either scanned, or entered manually in the order details, to the left of .... Confirm Collection.
A code should be sent per item.
Without this code, you cannot mark the item as dispatched. It can delay your payout for the item as delivery / collection cannot be confirmed. To a more serious degree, it does leave you open for the buyer to open a case of item not received.
In future , should you agree to a buyer's wishes to post a collection listed item, it's probably better to end the item and relist it with a postage cost.
@chduncan_13