[mholt]

https://zerossl.com/features/acme/

> Unlimited & Zero Cost

> In an effort to ensure the widest possible SSL certificate coverage around the world, our team has decided to keep all ZeroSSL certificates created using the ACME protocol completely free of charge.

[znpy]

Yep but that doesn't say that they won't rate limit, or what the rate limit is.

[mholt]

So you can either use a CA that has rate limits, or one that does not. It's up to you.