Is Stamp Duty payable on Amendment to the Contract

FACT:nWhile entering into a Contract, Parties evaluated and paid appropriate stamp duty and signed the Contract. A contract can be amended only by the parties participating in the contract. In the course of executing the Contract, the Party altered a few points/definitions in order to make changes in-line with the current developments.The Party issued an amendment, which was signed by both the parties.Issue:n1.Is this amendment to be signed on Stamp paper?n2.If so, then what should be the value of stamp paper?n3.If amendment is to be executed in counterparts (2nos.); what should be the value of counterpart stamp paper, on which counterpart amendment will be signed.4.What should the Party issue [Amendment / Addendum / Supplementary to Contract], to incorporate change in the Signed Contract?