Issue for resellers.
currently there is nothing to stop customers from adding unlimited domains to their plan, without your knowledge, which will cost you money, which the customer is not being billed for.
The only way to avoid this is to manually edit every customer after they are created and apply limits or set a custom permission group.
this is a PITA and requires someone remembering to do it for every customer, so if you forget, customer gets unlimited domains.

this needs to be fixed so that there are limits set by default on each plan (1 domain), ideally the ability to create custom plans as well.
Or at the very least if a customer adds another domain, it sends a request to the admin to approve it first.