Although I’m on the US beta, where I do have a routing number, and when I put in my details it just gives me a generic “Right now, we’re not able to complete this transaction.” error. No indication of whether it’s a PayPal issue or a Monzo US issue.
I faced a similar issue. When I reached out to Monzo, they said they were aware of this issue and would try to resolve it.
As far as I’m aware Monzo don’t support ACH in the US which is why you’re experiencing this error as PayPay uses this for debits/credits.
Ah. I’d thought it would work since I had no trouble linking Monzo to another bank account using ACH as well.