It is difficult to diagnose errors without the actual error message that the buyer is getting or an accurate description of what s/he is doing/seeing. There are multiple reasons why location would be an issue:
You might have your Buyer Requirements set to "Block buyers whose primary shipping address is in a location to which I don’t ship " and you don't have shipping set up to that country. Go to https://www.ebay.com/bmgt/buyerrequirements to see what blocks you have set and for a link to your log of those impacted by that (the link is in the wrong section of that page titled "Manage block settings and rules activity log" ) to see if the buyer is on it.
Look above the log link and see if you "Require buyers to provide a payment method . . ." for the activity in question. If they can't supply a shipping address in a location you have set up to ship to then eBay can't calculate how much to pre-authorize automatic payment for and so they can't bid/offer.
If eBay bots suspect that there might be an import/export restriction of the item between the two countries (and for the buyer's country that might be based on shipping address, registered address, or IP address) they will block the activity.
