If you receive the "Service unavailable" error when adding a bank account for United States (US) domestic withdrawals, this means one of two things:
(1) Your routing number is not Fedwire capable.
Kraken does not currently support ACH bank transfers.
(2) You have reached the limit of two bank accounts.
You are only able to have two domestic USD accounts on profile for withdrawals.
You can contact support if you need to have one or both of your existing bank accounts de-linked from your Kraken account.