Hello @psucolonel
Upon investigation, you can't offer one of your own International Slots for trade if you have unregistered International players in the squad that could otherwise be using the Slot.
If you are attempting to acquire a player that requires an international Slot or if they have an International player on the disabled list. In this instance, you have Tai Baribo on the disable list so you are unable to offer one of their International Slots for trade.
If Tai Baribo were to be released, you would be able to include an International Slot in a trade offer. Additionally, you can offer one of your International Slots for trade at any time if one of their International Players that is occupying a Slot is included in the trade offer.