Not sure, the closest thing I can think of would be captcha, considering how a lot of websites and services still employ said method to prevent bots. Even IP detection wouldn't work since that's easy to manipulate as well as other methods like email registration and whatnot. You can add additional requirements though, e.g. having a discord channel where you have a bot that verifies if they received something or not but again, this only elongates the process, not necessarily stopping bots from appearing.

There has been quite a few implementations of captcha from matching images, to typing the same letters/words to puzzles so maybe implement that and some additional requirements just to make it harder for bots to enter.