Either:
The seller has not set up shipping to the location of your primary shipping address (in My eBay: Account: Addresses) AND has set up a Buyer Requirement to block purchases by buyers with their primary shipping address in a location the item is not set up to ship to
OR the action you are trying to take (most likely a Best Offer rather than a "bid" on the auction, which are two different things) requires you to pre-authorize payment: there would be sections on payment source and shipping address on the confirmation page with links to change the default ones (e.g. your primary shipping address and payment source) and the one displayed is in a location the item is not set up to ship to (so eBay can't calculate the price for the pre-authorization)
OR eBay bots detect a potential export/import restriction for that item between the seller's country and yours (yours determined by your registration address rather than or in addition to your primary shipping address or the one you are trying to use to pre-authorize the payment.
