If the buyer has bought and paid for the item this is the best way to proceed now.
If this item was initially listed as a postage item, and now being collected, you will have no way to mark it as collected / delivered, and no proof that the buyer has collected the item as that all important collection code is not present.
Best way forward would be to cancel the item, citing Buyer Requests to Cancel, which refunds the buyer and to relist it again as a Collection Item only, for the buyer to buy again from your eBay listing.
Let the buyer know what you are doing but be very, very clear in your messages why you are delisting, that is, it's to relist for the buyer to buy from your listing, that this is Not an off eBay sale.
Buyer then buys and pays through eBay checkout, cash is no longer allowed for a collection item, and here the buyer receives that important collection code. You scan this code or enter the numbers manually to the left of Confirm Collection, this shows the item was collected , and will release your payout sooner.
@kel_chris8
