Mobile Deduction Over Limit

Hi All,

I am having a customer requirement which I need your help to Apply on SAP Payroll

The customer wants to set a mobile bill limit for each employee and if the mobile bill from the operator exceeded the employee limit, the employee is charged with the difference from salary

Ex:

1- If the mobile limit is 300 and mobile bill 250 ----> Deduction 0

2- If the mobile limit is 300 and mobile bill 300 ----> Deduction 0

3- If the mobile limit is 300 and mobile bill 500 ----> Deduction 200 (500 minus 300)

Please help me with the steps to implement this requirements