This was my final JSONstring:

{{
  "contact_name": "AutomationTestingF_PrajwalRaj",
  "first_name": "AutomationTestingF_PrajwalRaj",
  "company_name": "Insta",
  "email": "xyz@abc.com",
  "phone": "9999999999",
  "mobile": "9999999999",
  "billing_address": {
    "attention": "PrajwalRaj",
    "phone": "9999999999",
    "mobile": "9999999999",
    "pin": "232423",
    "zip": "232423",
    "address": "grerte rt erte"
  },
  "gst_no": "AAAAAAAAAAAAA",
  "gst_treatment": "business_gst"

}}

Here, Customer phone, email, mobile simply are not getting added while other details are. Need help