Check your Buyer Requirements https://pages.ebay.com/services/buyandsell/biddermanagement.html to see if "Block buyers whose primary shipping address is in a location I don't ship to." is checked. That is what usually prevents international members from bidding/buying. There are a couple of ways to have enabled that without actually going in and manually setting it. Buyers from countries you don't ship to but use a friend, relative, or commercial forwarding service in the US to receive the item and ship it on can change their Primary Shipping Address to the US address.
Occasionally there will be items where eBay's bots detect there might be a problem with export/import regulations between the seller's country and the buyer's (this seems to go by the buyer's Registration Address instead of or in addition to the Primary Shipping Address). Emphasis on "might be", it is often wrong.
If you mean that you opted into eBay International Shipping (EIS) and expect that it is on the listing, check the "Change location" dropdown on the Shipping, Returns, and Payments tab of the listing on the full website. EIS has its own exclusions (in general or to particular countries). https://www.ebay.com/help/selling/shipping-items/setting-shipping-options/ebay-international-shippin...
