Did you read ToS of the mixer? And besides most mixers always make sure to write the minimum amount that a user can mix at the top of the page during the process of mixing so there’s a high chance that you didn’t pay much attention to it.

As long as we don’t have the link of the site to verify if everything you have written here is correct or if you are the one that made an error and now you’re just trying to blame it on the mixer for now clearly stating the minimum amount.