Hi andrew41,
Try ticking PAYG exempt in the Pay Categories section of the Payroll Settings for the employee's specific pay category. Since you have created a PAYG adjustment prior, when a new pay run is created, it should only show the adjustment amount, not the amount that is automatically calculated.
To double-check this, also check the YTD figures of the employee to ensure that the automatic PAYG amount is not being applied.
Bonny