That's interesting. Happy to see it is sorted out for you. If you don't mind could you please share how you fixed it, if you remember it of course. Unfortunately for me I could not still get it working. I got in touch with both eBay and they first asked me to contact apple support. The first rep couldn't help me much, then she transferred it to their software support team. After some exhaustive inspection he said everything is fine from Apple's side and told me it has got to do something with Ebay since Apple Pay works for me perfectly fine on other websites.
After contacting Ebay's software tram it turns out that they have only enabled Apple Pay for iOS devices and mobile browsers at the moment. They said in the future they would enable Apple Pay for Macs soon. But I found a work around that if I loaded the item payment page on my iPhone and then I were to open it via the continuity safari icon on my Mac I'm able to get the Pay with Apple Pay option to show up on my Mac.
