Have you checked the customer invoice installment plan, that the bank account is connected there?

If the installment plan does not contain bank account, there will be no bank account in the customer invoice EINVOICE message.

You can set a default bank account in window Cash Accounts/ RMB Cash account per customer.

You need to use the Cash Account per Customer functionality. As Jan said, the IBAN and BIC codes are fetched from the cash account linked to the installment plan of a customer invoice. The proper Cash Account per Customer setup needs to be created before an invoice is created or you would need to go back to the invoice and select the cash account manually.

ABI code will be 5 characters of the bank account starting from the 6th digit.

CAB code will be 5 characters of the bank account starting from the 11th digit.

Regards,

Piotr