IBAN validation is too limiting for international transfers

I tried to send money (GBP to EUR) to a friend in the Netherlands. My friend provided 2 IBAN for 2 different accounts, and the app was not accepting either of them as valid.

Dutch IBAN is 18 characters, according to the Wise website:

2 letter country code
2 digit check number
4 characters from the bank’s bank code
10 digit code for the bank account number

I tried entering both IBAN with and without spaces, it didn’t work.

However when I used my Wise account separately from Monzo, it accepted the same IBAN that Monzo was rejecting and I was able to complete the transfer on the first try. So whatever is validating the IBAN in Monzo seems to not match with Wise’s validation