Can an Employee Fired for Performance During Probation Demand Their Pay? Seeking Advice!

One of our employees has been terminated from his services under his probation period, and now he is demanding the probation period amount from the company as mentioned in the appointment letter.

Is there any rule regarding employment that allows an employee terminated for performance issues to demand the probation amount?

Please suggest.

What is the probation amount? Please explain. During the probation period, the notice period is one day. Hence, is it one day's salary that constitutes the probation amount that you are referring to?