If an employee resigned, how do I declare $0 gross as they aren't earning anything.
You can choose not to pay former employee in upcoming pay runs.
Just to add to the above, I'd recommend that you add an 'End Date' to the employee's profile details.
What do you mean by this?
Set ‘Last Day’ in the employee’s profile, hopefully employee would disappear from the App in next financial year. The employee would still have an income statement for current financial year.