You will need to register and lodge a payroll tax return if the total Australian taxable wages paid by you or your group is more than $70,833 monthly or $850,000 annually. While your total Australian taxable wages are used to determine whether you are liable and the rate of tax applicable, you only pay tax on wages paid or payable in Western Australia.
Payroll tax is a self assessed tax. The onus is on you, as an employer, to ensure that any information you provide is correct and that you comply with your tax obligations.
A minimum tax rate of 5.5% applies.