How to buy tickets as a foreigner

Hi, I am from Italy and I will be travelling to the Netherlands for a little holiday and really wanted to watch the AZ Alkmaar home match in the conference league next week, I tried to get tickets from the website but they tell me I do not have access to buying the tickets.

Is there something I have to do? Or is it not possible for me to get tickets to the match?

Thank you for your help!