Why isn't a request sent to all sites?

Question

Python

Good evening.
I want to send a request to the site through the iPv6 proxy and get the response code.
When I send a request to the google.com site, the code 200 is returned.
However, if I send a request to the site https://2ip.ru/ or to the site https://steamcommunity.com/market/ , then an error occurs:

Traceback (most recent call last):
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\urllib3\connectionpool.py", line 594, in urlopen
    self._prepare_proxy(conn)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\urllib3\connectionpool.py", line 805, in _prepare_proxy
    conn.connect()
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\urllib3\connection.py", line 308, in connect
    self._tunnel()
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\http\client.py", line 907, in _tunnel
    raise OSError(f"Tunnel connection failed: {code} {message.strip()}")
OSError: Tunnel connection failed: 502 Bad Gateway

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\adapters.py", line 439, in send
    resp = conn.urlopen(
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\urllib3\connectionpool.py", line 637, in urlopen
    retries = retries.increment(method, url, error=e, _pool=self,
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\urllib3\util\retry.py", line 399, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='www.steamcommunity.com', port=443): Max retries exceeded with url: / (Caused by ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 502 Bad Gateway')))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\ilyam\PycharmProjects\steam orders bot\parse_id.py", line 65, in <module>
    r = requests.get(f"https://www.steamcommunity.com", proxies=proxies)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\api.py", line 75, in get
    return request('get', url, params=params, **kwargs)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\api.py", line 60, in request
    return session.request(method=method, url=url, **kwargs)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\sessions.py", line 646, in send
    r = adapter.send(request, **kwargs)
  File "C:\Users\ilyam\AppData\Local\Programs\Python\Python39\lib\site-packages\requests\adapters.py", line 510, in send
    raise ProxyError(e, request=request)
requests.exceptions.ProxyError: HTTPSConnectionPool(host='www.steamcommunity.com', port=443): Max retries exceeded with url: / (Caused by ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 502 Bad Gateway')))

The code:

import requests

proxies = {
    'http': 'http://oOAQ6o:[email protected]:4002',
    'https': 'https://oOAQ6o:[email protected]:4002'
}

r = requests.get(f"https://www.google.com", proxies=proxies)
print(r.status_code)  # 200

url = 'https://steamcommunity.com/market/listings/730/AK-47%20%7C%20Elite%20Build%20%28Field-Tested%29/render/?query=&start=0&count=100&country=RU&language=english&currency=5'

r = requests.get(url, proxies=proxies)
print(r.status_code)  # error
print(r.json())

Why is the request successfully sent to the google.com page, but not to the steamcommunity.com page? How can this problem be fixed?