This is a known problem with Nordea Bank IBANs.
The bank/branch code used for domestic validation is not the same as the bank/branch code used in a Nordea Bank IBAN.
This is because the bank codes used in the IBAN may not be current bank codes. However they are correct when used in the IBAN.
We have been advised by the Finnish Bankers Association that only the bank can provide the correct IBAN for Nordea Bank customers.