When you make an international transaction, the characters that make up your IBAN are passed through your bank's payment system. By comparing the numbers and letters to the sender's and recipient's data, the system can verify the sender's and recipient's accounts.
Special techniques are used to evaluate and check the account information. If the payment is legitimate, it will be processed.
The transaction will fail if an IBAN is supplied improperly and there is no account associated with that IBAN. The transfer will go through if a corresponding account exists, and the bank can only revoke the transfer with the recipient's approval.
However, you shouldn't be concerned because most banks use an IBAN checker to ensure that genuine IBANs are error-free.