@agentcloseteur
This is probably something best reported to eBay at the buyer's end, since the buyer is the one that sees the error message.
Problems with the eBay app can be reported by shaking the device while the app is active. That should allow eBay to get lots of information about the state of the app directly, which may help in diagnosing the exact issue.
If I were having this error as a buyer, I would try to accept the offer again using a browser -- preferably a desktop browser. I would first attempt to make sure the cart was entirely empty to start with, and that a purchase was not previously committed to at full price already. If there is a "Pay now" link in the Purchase History for the offer, that may work differently than the original offer-to-cart interaction (not sure, but worth a try).
If I was unable to empty the cart, but the item did not appear in my Purchase History as "awaiting payment" (indicating a committed purchase), I might try again to accept the offer on ebay.ca instead of ebay.com, as each country site has its own cart system. In the past I have found that some transactions that failed on ebay.com were able to complete successfully on ebay.ca instead.
Sounds stressful and frustrating for both buyer and seller alike. Good luck to you both.
