There can be several reasons why this might happen.
Some of our users received new IBANs that start with 'LT' instead of 'GB' at the end of last year due to Brexit. We made it possible to use both 'LT' and 'GB' IBANs to receive transfers, but this was temporary. Inbound transfers to old account details with 'GB' will fail and the senders will receive the funds back within 5 business days. If this happened with your transfer, please make sure to inform your counterparty that your account details changed.
Another possible cause is that, due to compliance reasons, we're unable to accept deposits by transfer from certain sources. This includes some cryptocurrency exchanges, certain countries, banks, and entities. We're also not supporting the following route of deposits by transfer:
If your deposit wasn't successful, the funds should be reverted and returned to the sender’s account within the next 5 working days.
Lastly, if you tried to add money by card and it was reverted, it might be because you didn’t complete the 3D Secure authentication or there may have been a connection issue - try again.