The Employee's leave balance will be the Forecast balance less any outstanding leave applications. The leave will forecast by default to today but this can be changed.
If the leave has been accrued to a date after the Forecast Date in MicrOpay, the Leave will be the balance from MicrOpay. You can see this value in Balance of last pay when you expand the Leave Type. The expanded view will also display Not yet paid and Not yet approved hours, which are the hours from your outstanding leave applications.
An Employee may appear to have a negative Leave Balance if the total of all future leave applications (that haven't been processed) is greater than the Forecast balance. This could be because the Forecast is to today's date but there are future leave applications.
For example, an employee's Forecast balance is 10 hours as at today but they have applied for 2 days leave (15 hours) in three months, the balance will show as -5 hours. However, in three months, they will have accrued enough leave to cover the application.
You can change the Forecast Date to the end of the Leave Application to check if they have enough to cover their application(s).
Note: Leave can be set up in ESS to allow employees to exceed their balance. To check, go to Settings, Leave, and check Allow insufficient balance.