If you started processing STP mid-year and you had seasonal workers who worked prior to this you can run an update event to send the year to date information to the ATO- https://quickbooks.intuit.com/community/Payroll-and-STP/Create-and-lodge-an-update-pay-event/m-p/275…

You can also apply for a deferral via the ATO Portal:

Resolution for 'ATO Portal issue: 'How do I set up a seasonal employee for STP? In this instance, they only work two months in a year' available: Yes.

The ATO Portal issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the ATO Portal issue yourself by looking for a resolution described in the article. If it is a complex ATO Portal issue or you are unable to solve the issue, you may contact us by clicking here or by using other ATO Portal support options.

For more information about resolving issues related to ATO Portal in Quickbooks/QBO or to get support for the issue 'How do I set up a seasonal employee for STP? In this instance, they only work two months in a year', click the link below: