See posts by @Tut at Cash vs. accrual P&L and Payroll expense which includes:
Manager is, at its core, an accrual basis system with options for cash basis reporting. But if you intend to use cash basis accounting, you need to adapt your procedures for when you record expenses.
In your example of paying an employee in April, you should not enter the payslip until April, then immediately pay the employee. You are right to guess that payroll is somewhat different. A payslip tells the program that you have incurred expenses for wages or salaries. These debit an expense account and must be matched by a credit to a liability account, Employee clearing account. But no money has moved. So there should really be no entry at all if you are not paying the employee.
Technically, a purely cash basis balance sheet would not include accounts like Accounts receivable or Employee clearing account. But many of Manager’s functions would then not work.
So in short in your case you can only issue the payslip on the date of payment when you use cash accounting.