SmoothPay caters for contractors/agents who may have requested tax to be deducted from their payments (tax code WT). Setup as follows:
You control how GST is to be catered for (for accounting purposes) in Company Setup. There are options to treat amounts entered as inclusive/exclusive, and if GST is to apply to Time earnings (by default GST will apply only to allowances that have been set to one of your defined GST rates)
GST rates can be set/changed in Payroll Codes - these should already be correct at 15%
If you're paying the contractor using an allowance code (e.g. Harcourts Group pay all sales agents via allowances) then any allowance codes you have can be checked and set to use any of the GST rates you have configured.
NOTE: GST won't apply to staff unless they are set to have GST calculations in their employee setup.
There's also an option to omit GST from GL Costing journals if it has already been accounted for in your General Ledger (rarely used).
Set the employee up as a contractor with tax code WT and set the percentage required in their tax settings, set their GST option to GST on Payslip or Buyer Generated Tax Invoice (depending on whether he gives you an invoice or you are going to generate one on his behalf).