If there are too many incorrect attempts at entering in the PIN, CVV, expiry, or other card details, for security purposes the card will get automatically blocked.
To resolve this all you'll need to do is the following:
Log into your Vault account
Head to the Cards tab
Select the card that is locked
Click Settings
Click Unblock
Please note, if it was a physical card that was blocked there will be a couple additional steps after completing the above:
Once the card has been successfully unblocked you'll need to make a chip and PIN purchase by inserting the card into a terminal
When you first insert the card after unblocking, the terminal may automatically decline the transaction. This is expected and part of the process to unblock the card.
Re-attempt the same transaction and insert your card, you'll now be prompted for your PIN and once entered correctly the card will be fully re-activated