Have you looked in your email >> Bin and also Spam? It might be sitting there.
Or, send the buyer a message if they could kindly send you the code, they should be able to see this in their order details, email or eBay message. Then, you can manually add those numbers alongside ..... Confirm Collection.
If the above is not possible, you will have to wait a minimum of 14 days before the payout for that item is released.
@fluffybull