If a pending amount is showing on your FairFX card this will be the total value of all the pending transactions on the FairFX card (shown on your statement as 'Auth'), i.e funds which have been spent but not yet banked by the merchant. 

Merchants can take a few working days to bank the money from the card, therefore the money is ring-fenced so that it cannot be spent elsewhere. When a merchant finalises the transaction, the 'Auth' will become 'Fin' and the amount will be deducted from the 'pending' balance.

Please just ensure that the 'available balance' covers the amount you want to spend on your card as this is the amount you have available to spend.