422
merchants.invalid_bank_accountmerchantsRule R6The bank account details are not valid
bank_code must be one of the Thai bank list, the account number 10 to 15 digits, and the holder name present. The number is stored encrypted with only its last four digits in clear, so it cannot be read back.
Why the API refuses
WHEN AddBankAccount is executed, THE SYSTEM SHALL reject it unless bank_code is one of the Thai bank list, the account number is 10 to 15 digits and the holder name is present, SHALL store the account number encrypted with only its last four digits in clear, and SHALL make the first account of a merchant its default.
What to do
Strip spaces and dashes from the account number before sending it. Use the bank codes from the reference rather than a bank's display name. The first account added becomes the merchant's default automatically — you do not set that.