I think that another way should be found to prevent the registration of possible scammers on this forum.
This forum is all that Pmalek mentioned but even more than that, a place where people meet and become lifelong friends.
This forum is a community of people who have the same or similar values, ideals and thoughts and should be open to everyone.
In addition to limiting by IP address, it is quite possible to calculate the number of your users through browser fingerprints. Probably everyone knows that browsers leave thousands of fingerprints in our systems, which remain in memory for a long time. And if some prints, especially smart users, can fake and change, that is, those that are almost impossible to change.
Using this system, you can easily ban fraudulent accounts on the forum, given that not everyone is ready to change their hardware for the sake of registering on the forum.
https://pixelprivacy.com/resources/browser-fingerprinting/