eBay started redirecting users to the mobile version of checkout a while ago, whether they are on a mobile device / using the app, or not.
As you can see in the screenshot, it has the 'pay.eBay' part of the URL and shows it's a redirect to mobile checkout. (I've said it before, but I'll say it again.... I hate it, so much so that I won't use it. At all. I have a workaround to get back to the normal checkout, but it only works with Aus listings. The seller or item doesn't have to be in Aus, but has to be listed on the Aus site so that it's in AUD - you need to keep an item in your cart from a seller that has other payment options, then when you go through checkout, click 'see more payment options'. That will take you to the normal site checkout, then you can click 'Pay only this seller' on the item you actually want to buy).
