If you receive the "Service unavailable" or "Internal error" message when adding a bank account for United States (US) domestic withdrawals via Synapse, this means one of two things:
(1) Your routing number is not FedWire capable.
Kraken does not currently support ACH bank transfers for deposits and withdrawals.
(2) You have reached the limit of two bank accounts.
You are only able to have two domestic USD accounts on profile for withdrawals.