It is a legislative requirement that employees get a paid day off on public holidays, but if your employee works on this day and if it’s an otherwise working day for them (a day that they would have normally been at work) they are entitled to be paid time and a half and to be credited a day of Alternative Holiday. If it is not an otherwise working day, they still need to be paid time and a half but are not technically entitled to an Alternative Holiday.
iPayroll has a public holiday calendar in the system and each time you open a pay, if a holiday falls within the pay period; you will see a notification on each timesheet. If you determine that it is an otherwise working day for an employee and they worked, you can add it to the timesheet as PHW - Public Holiday (Worked).