See if you, or your son if he has access to your account, can change the tracking . Go to item sold >> View order details >>Postage>> Track Postage drop down arrow and change the tracking. It's preferable to use a laptop / PC for this , and with Chrome, that seems to work best.
If this is not possible, then your payout will be held for a minimum of 14 days, there's nowhere for a buyer to mark received. They can leave feedback but this releases payouts sooner only if the item is £25 or less in value.
If as this seems to be a Simple Delivery item, the buyer usually pays for the label, they will be refunded for the unused label in 30 days. If you marked it ' Seller pays for postage' , find your label with this link . https://www.ebay.co.uk/ship/lmng/labels-history/seller-hub and to the left of the sales record there is a drop down menu under 'Actions' click on that , then click on 'Void Label'. You need to do this within 14 days.
@stwinifreds