Need to show cash discount in Invoice

When i enter discount in Payment-in voucher, it is not displaying in invoice.
Invoice showing wrong received amount.
example:
Invoice amount: Rs 2020
Received amount Rs 2000
Discount: Rs 20

Currently invoice showing as Rs 2020 received. It is wrong.
Actually received amount is Rs 2000.
Kindly correct this.
sharing screenshot of my invoice (click below link):

https://drive.google.com/file/d/1LeKs2zHfRKOCpjvDARXiaZpw_wqW4gqF/view?usp=sharing