The IBAN number of the account I want to transfer money to is NL99 INGB 9999 1234 99. When entering these details in the my online banking portal, do I have to insert spaces as shown or type the 18 characters in a row?
The spaces are not part of the number and are just used to group digits. Some websites allow you to type the spaces and will remove them automatically, other sites consider spaces invalid.
Don't worry, if the number is mistyped the website will show an error. IBANs also include an error detection code that ensures that you didn't mistype the number.