Hi @info17721 ,
There is no specific error code or instruction to provide for this, as they would need to reach out to the bank to gather more details specific to their bank account details. I checked with my internal tools to locate the transaction for any additional information, but the charge does not show.
The best thing would be for the client to reach out to their bank. There were issues with the payment method MercadoPago and PayU but this does not appear to be the case, there are no other reports of this. If your client confirms with their bank there was no issue with this charge, please open up a support ticket to further investigate, but I do believe it may be a preventative measure from the bank of some sort.