APP-PAY-06346 error is common in HRMS module so need to take given necessary action to resolve this error.

Follow the below steps to resolve the error :

1. Find the person in question
2. After the effective date (Calendar page on the tool bar) to a date before the termination, say 01-JAN-2020.
3. Alter the assignment as needed
4. Save the change. There should be no error as long as there are no changes between this date and the termination date.
5. Migrate the solution as needed to your other instances.