Everything you need to know about STP and more - https://www.ato.gov.au/Business/Single-Touch-Payroll/In-detail/Single-Touch-Payroll-employer-reporting-guidelines/?page=5
If a related entity will be submitting STP reports on behalf of other ABNs within a group, that entity needs to have a business appointment to lodge on your behalf.
This business appointment can be completed in two steps:
1. Use the Cross entity authorisation nomination form (NAT 73957) to nominate another ABN to act on your behalf.
2. The AUSkey administrator for the business must assign the appropriate role to the authorised AUSkey holder.