The number of staff members that you can add to Kayako depends on the seats your purchase. Please note that if your staff count in Admin CP exceeds the purchased seats, your helpdesk will become inaccessible. You will need to contact Support to resolve this issue. If you are on Download subscription, you can try the following steps to disable extra staff members from the database.
UPDATE swstaff SET isenabled = 0 WHERE fullname = [Full name of any of your staff members in your helpdesk]
DELETE FROM swregistry WHERE vkey='staffcache';
Please note that ‘Disabled’ staff accounts would not count towards the total count.