To add the reason and mode of termination of the contract in the employment document:

Enter the end date of employment in the END OF EMPLOYMENT field. After entering the date, two additional fields will appear: REASON FOR TERMINATION and MODE OF TERMINATION. Fill in these fields.

If the system has mandatory completion of these fields enabled, then after entering the end date of employment (current or in the past), filling them in will be required before saving the document. In the case of a future employment end date, the requirement does not apply, and the document can be saved without completing these fields.

You can find more information on this topic in the article: Work termination reason and modes.