A couple of weeks ago I tried to switch my Vanguard direct debits to my Monzo account. I got a message back saying that they couldn’t verify the account details and wanted me to upload a bank statement. I couldn’t be bothered at the time so I just switched the details back to where the payments were coming from before.
I’ve asked them now why there is a problem, and will let you all know the response. I wonder if this has been raised before regarding Vanguard?