I’d suggest looking at 3 things:

1. CAPTCHA. Not a perfect solution and AI will beat most of it soon, but it will help.
2. Anti-bot tools. Something that will do the equivalent of miring up AI web crawlers.
3. Identity systems. Not in the sense of a verifiable ID like a driver’s license, but in the sense of establishing a strong link between a pseudonymous ID and the community it owns or interacts with.

https://www.tendenci.com/

It’s membership association software. It includes modules for membership payments and donor payments.