reformat t parameters to json string

How we can use  AttributesToJSON process to reformat the n1,n2,n3 parameters to json string as below ?
{
  "n1": 20,
  "n2": {
    "n3": "1400000474"
  }
}     

we try to do that but the output of json string coming with \" , we want to pass the output of AttributesToJSON process to postHttp process
{
"n1" : "20"
"n2" : "{\"n3\":\"8001001922\"}",

}