The Spanish are probably trying to get an 'IBAN' number, not being aware that the system is not universal, or insisting on it out of stubbornness/arrogance...

International Bank Account Number - Wikipedia, the free encyclopedia

Thai banks do not use the IBAN system and you need to get this information through to the Spanish bank.

If you are being sent foreign currency, you may need to contact Kasikorn to ask which handling bank (correspondent bank) they have for that currency.