Tibia Coins can only be sold in the Market or gifted to other characters if they are transferable.
Tibia Coins which are not transferable can only be used to purchase things for your own account in the Store.
Whether Tibia Coins are transferable or not depends on the selected payment method, the amount of Tibia Coins you want to order, and certain account criteria. After placing an order, you will see whether your order for transferable Tibia Coins has been successful. If you are not allowed to purchase transferable Tibia Coins with the selected parameters, you will have the options to either purchase Tibia Coins which are not transferable, or to try a different payment method.