You will have received a notification from IRD to deduct an amount each pay for one of your employees. You are required to do this by law. iPayroll has a standard Pay Element - Child Support Deduction - CSD Element. If you are not able to use this as you are required to direct the amounts to a third party bank account you will need to set up a new Pay Element - Child Support Arrears - CSD ARR.
Check the details of the payday and pay period on the notice, if it is incorrect you will need to contact IRD.
They can amend the amounts to deduct during the year.
Child Support has priority over any other deductions after you deduct PAYE and KiwiSaver.
The date you must start deducting is stated on the notice