Hi there, @gerrardscross.
If you have already run payroll for a specific period, you cannot delete any SSP included in the pay run. An error message stating, "You can't delete a leave if you've already run payroll for that period" will appear if you attempt to do so.
This error message indicates that you are attempting to modify SSP during the dates of a pay run that has already been finalized in QuickBooks. To resolve this issue, you have two options: revert the pay run or delete the draft. Only after doing so can you delete the SSP from the employee's profile.
For example, you have a completed pay run that covers the pay period starting from 1 to 31 August. The first day of leave for an employee's SSP falls on 27 August and the last day of leave is left empty. If you want to set the last day to 31 August, you'll need to roll back the pay run before you can edit the SSP in the employee's profile.
I'd also recommend contacting our Support Team to get answers to your questions about this matter. They can provide an accurate resolution according to your scenario.
For more information about recording, editing, and removing SSP, refer to this article: Statutory Sick Pay (SSP) in QuickBooks Online Standard Payroll.
Read about Statutory Sick Pay (SSP) in QuickBooks Online Advanced Payroll to know more about the legal minimum you must pay your employee.
Feel free to post here again if you need anything else in the program. I'll be here to help you.