I have huge nested JSON that is being fed as a n input to the API. The input JSON looks like:

[{
  "ID": "123456",
  "accountNumber": "876545",
  "contractType": "ABCD",
  "linedata": 
    {
      "productSKU": "1234",
      "data": {
        "Line_Number": 1726428,
        "Reservation_Number": "1726428",
        "Quantity": 1,
        "UnitPrice": 16,
      }
    }
  },
  {
  "ID": "345678",
  "accountNumber": "445566",
  "contractType": "ABCD",
  "linedata": 
    {
      "productSKU": "2345",
      "data": {
        "Line_Number": 3213445565,
        "Reservation_Number": "123456789",
        "Quantity": 1,
        "UnitPrice": 25,
      }
    }
  }] 

I need to convert this into a CSV flat fromat retaining the JSON elements for linedata attribute which looks like:

Data, ID, AccountNumber, Contract_Type
{"productSKU":"1234","data":{"Line_Number":1726428, "Reservation_Number":"1726428", "Quantity":1,  "UnitPrice":15}}, 123456, 876545, ABCD
{"productSKU":"1234","data":{"Line_Number":1726428, "Reservation_Number":"1726428", "Quantity":1,  "UnitPrice":15}}, 345678, 445566, ABCD

The problem is that when I try to concatenate the linedata attribute as string, I am left with backslashes in the output and all my attempts to remove those bacslashes have gone in vain. Seems like I am missing something basic here. What is the best way to achieve this ?