After adding the modification in single line item that would not displayed in payment page and also that price is not added in order total amount:
final response Json:
LineItem{json='{"createdTime":1537529892822,"modifications":{"elements":[{"amount":1122,"name":"sample 1"}]},"taxRates":{"elements":[{"id":"1TNR2D254V4QM","taxAmount":0,"rate":200000,"isDefault":true,"name":"GST"}]},"userData":null,"alternateName":"","exchanged":false,"id":"2NFCZKPY3NMSR","refunded":false,"price":121200,"binName":null,"isRevenue":true,"name":"df","item":{"id":"R12SFS93S4Q5R"},"printed":false,"itemCode":"df123"}', bundle=null, changeLog=Bundle[{modifications=null}]}
