As long as you don't view a card's digits on the Requests page, the card doesn't expire.
Single-purchase cards expire right after the settlement (i.e if a payment has been initiated) or 4 days after the first banking authorization even if there is no charge in the end.
They expire 15 days after the first generation date if they are not used (i.e if you open the card details and do not use the card in the next 15 days).
Single-purchase cards are valid until the last day of the following month: for e.g., if you generate a single-purchase card on September 8th, it will expire on October 31st. You won't be able to use it after then.
➡️ In some cases (car rental, travel, hotel booking...) it's therefore best to use a recurring card.
Cancellation / Failed transaction
If an authorization is cancelled for any reason after being authorized, there will be no charge. Funds will go back to the company's available account. Charge is due within 18 days, above this time the authorization is cancelled (32 days in extra-rare cases).
This is why sometimes payments appear as "pending" for a while before being cancelled.
Settlement: a payment is made when the merchant confirms the transaction, usually 1-4 days after authorization. It then moves from "pending" to "payments of the month".
From 'Requests' to 'Payments'
A request disappears from the Requests tab after the first authorization was made on the card, and it shows in 'Payments'. Usually, virtual cards get blocked quickly after they are used. That's why sometimes you might need to generate a new card if a merchant has refused your payment, as the card appears as "used" already.
In most cases of purchase, the merchant checks the validity of the card with 1 or 2€ tests. Then they charge the card with the amount of the purchase. Sometimes, the budget is not enough to cover the test + the purchase so we recommend to always set up a slightly higher budget.
More info here.