With no collection code, therefore no proof the item was collected, the eBay can hold your payout for that item for a minimum of 14 days. The hold can be longer if you are a new or returning seller.
If you sell another item for collection, after payment send the buyer a polite reminder that they must bring with them the collection code, that the item will not be released without it.
One good thing in your present case, if the buyer sent a courier, they lose eBay's protection under the 30 day MBG Money Back Guarantee policy for item not received. Sending a courier / third party invalidates that protection.
@cdjcarsbristol