ATO is sending reminders to all known employers that have not yet started STP reporting. This is a Good thing.
However; Closely Held employees do not have to start reporting until 1 July 2020. There is no way to tell the ATO or is there....
To notify the ATO or more to the point to stop them hassling you and your client consider "applying" for an "exemption". Then down in the Reason box select "Other" and then state "Closely Held Employees only"
It isnt the ATO approved way but they have not given us an alternative.
From the ATO Fact sheet about closely held they state
"If you have 19 or less employees, you will not need to report closely held payees through STP in the 2019–20 financial year."
If an employer has both closely held and external employees then you must report for the external employees now and the closely held can be brought in later.
ATO Fact Sheet for Closely Held pdf
ICB Single Touch Payroll Resources