Don't eBay issue you with a courier label when an item is being sent to the authenticator, and isn't the tracking label uploaded automatically, or did you have to add it to the order details when you dispatched your item?
UK buyers pay a flat £8.95 eBay postage fee when purchasing sneakers that qualify for Authenticity Guarantee. We'll then send sellers a pre-paid DPD postage label so they can post the sneakers to the authentication facility, free of charge.
Taken from:
https://www.ebay.co.uk/help/selling/selling-tools/selling-authenticity-guarantee?id=4644&st=3&pos=1&...
