I want to convert Google IAP Receiept to String?

I want to change the response from the google IAP unity
From this:
"{"Store":"GooglePlay","TransactionID":"Example","Payload":"{\"json\":\"{\\\"orderId\\\":\\\"Example\\\",\\\"packageName\\\":\\\"com.Example.Example\\\",\\\"productId\\\":\\\"Example\\\",\\\"purchaseTime\\\":Example,\\\"purchaseState\\\":0,\\\"purchaseToken\\\":\\\"Example\\\"}\",\"signature\":\"Example\"}"}", "transactionDate":"Example"}

To this format:
"{\"Store\":\"GooglePlay\",\"TransactionID\":\"Example\",\"Payload\":\"{\\\"json\\\":\\\"{\\\\\\\"orderId\\\\\\\":\\\\\\\"Example\\\\\\\",\\\\\\\"packageName\\\\\\\":\\\\\\\"Example\\\\\\\",\\\\\\\"productId\\\\\\\":\\\\\\\"Example\\\\\\\",\\\\\\\"purchaseTime\\\\\\\":Example,\\\\\\\"purchaseState\\\\\\\":0,\\\\\\\"purchaseToken\\\\\\\":\\\\\\\"Example\\\\\\\"}\\\",\\\"signature\\\":\\\"Example\\\"}\"}", "transactionDate":"Example"}

 

The first line looks like a json string that is returned, so it's already a string. Why do you need to convert it further?

 

https://msdn.microsoft.com/en-us/library/fk49wtc1(v=vs.110).aspx