Monzo users have been left unable to use their card for payments or transfers following a technical problem with the banking service.
The digital bank posted on X it had "identified some issues" and activated a stand-in backup service which meant users could still make transactions like card payments and sending and receiving bank transfers.
However, some users noted under the post that Monzo Stand-in was "not working as expected" and they could still not use their card.
The firm added it was "rolling out a fix and moving quickly to get full service back up and running for everyone".
The British digital bank was set up in 2015 as a "new kind of bank" that ditched physical bank branches for a mobile-first app.
The firm says it now has more than 16 million personal and business customers which use the service around the world.
As the company works on the issue, it noted that users would be able to use its independent service Monzo Stand-in to still "make card payments, withdraw cash, freeze your card, send and receive bank transfers, and more".
While the support appears to be working for some, others have still been reporting issues.
"I can't use my card for anything at the moment," posted one X user.
"Your "backup" bank does not have the functionality you state it does. I can't make bank transfers right now," said another.
