{'code': 4, 'message': 'Invalid value passed for JSONString'}

{'code': 4, 'message': 'Invalid value passed for JSONString'}

Even after url encoding getting following error
        payload = {'JSONString=': {"contact_name": data['contact_name'],
                                  "billing_address": data['address'],
                                  "shipping_address": data['address'],
                                  "contact_persons": [{
                                      "email": data['email_id'],
                                      "first_name": data['contact_name']
                                  }]}}

        headers = {"Content-Type""application/x-www-form-urlencoded",
                   "Authorization""Zoho-oauthtoken " + access_token}

        r = requests.post(url, data=urllib.parse.urlencode(
            payload), headers=headers)
        r = r.json()