You can require address as part of credit card validation.

So only people with credit cards are allowed to use the forum? That shuts out a lot of people, especially in places where credit cards aren't used.

You’re right that credit cards are not a universal MOP (method of payment). Other options include debit cards, or systems like iDEAL, PayPal, etc.

Right, and those completely vary from country to country. Trying to get one website to support the common authenticated payment systems worldwide is basically impossible unless that website is Google.com.