Additional Information Column On Payment Page - Customer VAT No - Changing Optional To Mandatory

Hello Everybody,

I am writing for Italy. I have a question, my accountant asks me to add VAT numbers (codice fiscale in Italy) for all customers but on my payment page it is is optional. I checked everywhere but couldn’t find anywhere to change it to mandatory. Can you please help me how I can change this?

Thank you so much

Zehra Bural