@whitepeopledancing, you're right, the popup doesn't stipulate but it does say "T&C's apply" as a link. You need to click on that T&Cs link so I'm pretty sure that it complies with ASA regs. This is a screenshot of the popup.
How it works is, you're on the full website version of ebay and add something to your basket. That triggers this popup to appear. The voucher will already be on your My Ebay Summary page but you may not have been on that page to notice it, hence the popup. The QR code is just a link to the app, you don't need to use it as you can just get the app on your phone the normal way.
If you click on the T&Cs, you get this page: Terms & Conditions App Coupon | eBay.co.uk which tells you that the voucher and its terms are on your My Ebay Summary page. Here's the direct link to that page: Summary | Myebay | eBay
Below is a screenshot of my own summary page which currently has a voucher at the top (code blanked out as it's mine and I'm using it).
Like anything, there's always T&Cs and I'm guessing ebay, like any other big company, will make sure they're just the right side of legislation.
You can always see if you have any active vouchers by going to your My Ebay Summary page using the link above. You don't need to wait for a popup. Any active vouchers and their terms are always there.
Once you've seen that you've got a voucher, you can add items to your basket on the full website then go on the app just to checkout and pay if you want. Once items are in your basket, follow my instructions at post #18 above.
It's actually a pretty good saving if you do have fifty quid of items to buy as it can be used for multpile cheap items checked out together to make the fifty quid, not just one single £50 item.
