How to process allowance that differs every month

For example, the income for employee as below:

Basic salary:RM1700
Monthly fixed petrol allowance: RM300
Shipment allowance:RM200 per day (depends on number of days that the employee has attend the shipment, Not fix)

So my question is, how to add the non fix shipment allowance into the employee’s salary?

Add an Earning item, then add this item to Employee salary profile. Upon running payroll process, change the Quantity.

For further details, kindly do some simple test yourself to see how it works.