Probably best to try to speak to someone at ebay. Although you could buy postage online and send the QR code to the buyer it won't be linked to the return so see what ebay say.
Click on the help link at the top of any page. Select a topic (doesn't have to be the right one) then scroll down to Contact Us. Get to automated assistant and put in the question box Can I speak to an agent? or similar. And repeat until they pass you to a real person. The mornings may be better for getting through.
@limited2art_art_and_sculpture_gallery