bug: error message "JSON parse error..." after REST-query to add-to-cart?format=json

environment: OS xUbuntu 18.04.4; Python 3.6.9; Django 3.0.8; django-shop 1.2.2 (installed according to instructions https://django-shop.readthedocs.io/en/latest/tutorial/intro.html) STR:

1. get cookie-values csrftoken and sessionid adding 1 product to cart in browser and parsing them from headers of corresponding http-request
2. execute Python-code (adding 1 products unit to existing cart according to instruction 17.2.3.3. Add Product to Cart)

import httplib2
from urllib.parse import urlencode
h = httplib2.Http('.cache')
data = {
  "quantity": 1,
  "product": 15,
  "product_code": "1004"
}
data = urlencode(data)
response, content = h.request('http://localhost:8000/catalog/smart-cards/sdxc-card-64gb/add-to-cart?format=json','POST',data,headers={'Content-Type':'application/json','accept':'application/json','Cookie':'csrftoken=3hoZkpJNer2kSNaDgO3nOa8r2fLNl6KiwtMJDCW5pbDN9jELORM2dDIYCnE8wwew;sessionid=2k0t3edvimyud5acdpvt71e5dda7jod7'})
print("response.status  -  {0}".format(response.status))
print("response.items()  -  {0}".format(response.items()))
print("content  -  {0}".format(content))

AR: content - b’{“detail”:“JSON parse error - Expecting value: line 1 column 1 (char 0)”}’ ER: understandable error message in the response body

[jrief]

as far as I know, JSON data must be transferred (and will be received) as byte-stream, not string. Maybe you have to check this as well.

[jrief]

before sending a dict as JSON, you have to stringify it.

...
import json
...
data = {
  "quantity": 1,
  "product": 15,
  "product_code": "1004"
}
data = json.dumps(data)
...