You may get this error message on the attendance info page, "Employee is not assigned to any attendance scheme/shift" if the affected employees are not aligned to any shift or attendance scheme on the Position History page.
Step 1 - Navigate to the Position History page from the Employee Information section
Step 2 - Select the Employee, then click on the edit button next to the Attendance Scheme or Shift Category
Step 3 - Add the New category , Save the changes
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