FrappeClient: Insert row on child table

Hello,
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"}}
client.update(update_form)

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