To add a one-off payment:
Search for the employee and go to their profile.
Click Payroll and select Pay.
Scroll down to One-off Pay Adjustments and click either Add One-off Payment or Add One-off Deduction.
Enter the date for the payment and select the pay element from the Item list.
Enter the cash value in the Addition or Deduction fields.
Click Save.
The payment will then be exported to Payroll with the following export and paid on the date that has been entered at step 4.