Another reason is that the employee is set to 'Do Not Withhold' by mistake. Here's how to check and update it.
From the Payroll menu, select the employee's name.
Click Edit employee. Under the What are [employee's name] withholdings section, tap the Pencil icon.
Make sure the federal status is not Do No Withhold (exempt).
Tap Done to save it.
We also have to consider the wage base limit. It is the maximum wage subject to the tax for the year. Please check this article for your reference: Payroll tax wage bases and limits.
You'll want to run the Payroll Tax and Wage Summary report to see the wage base limit. Search and pull up this report on the Reports menu.