It’s not about setting 0, the problem is about the empty field.
I’ve set the minimum price, and it perfectly works, because if someone sets 0, the alert of the minimum price appears, and automatically sets the minimum price in the amount filed.
Otherwise, if someone doesn’t set anything in the amount field, the field remain empty and it goes on with 0$ donation.
So what is needed is a check of the “wpneo_donate_amount_field”, and if the field is empty the donation button shouldn’t be clickable.