FrappeClient: Insert row on child table

As per title, how to do so?
I have try by inserting new row to the Child Table. However, i got this error in return:

Following is my code

update_form = {"doctype": "Doctype A",
   "name": "c044972581",
   "item": {"item": "abc123"}}

that means that your server did not recognize, you are sending the wrong request message. try following can be found in frappe-client/ at master · frappe/frappe-client · GitHub