Virtual Cards are prepaid debit cards. It can only be used up to the balance available for your company and specific card.
Available Balance for a Virtual Card can be found on the Virtual Card details page.
Spent (in red): Any payments with the card appear immediately as Spent, regardless if it is pending or completed. Declined payments are not included.
Remaining (In green): Available amount on the card to be spent. Remaining amount = Spend Limit minus Spent.
If the Available Balance is insufficient to make upcoming payments, you can update the Spend Limit of the card.