There are a few reasons why income tax is not generated. One of the reasons is, the employee's income has not reached the income tax bracket. But if you confirm the employee is taxable and you encounter errors when processing this employee in payroll, please do as follows:
Go to the Payroll module.
Click Modules and select Income Tax.
Select Income Tax Details.
Check if you can search for this employee's record.
If the employee's record does not exist, you need to delete this employee at the Core module, Personnel Details. Then recreate this employee again.