Python requests 'SSLError: [SSL: WRONG_VERSION_NUMBER] wrong version number' (HTTPSConnectionPool, Max retries exceeded, ProxyError): why does it happen and how do I fix it?

Cause: Python's TLS layer started a TLS handshake and the other end answered with something that is not TLS, usually plain HTTP. In practice this means one of: you used https:// against a port that serves plain HTTP (for example a development server or an internal API); a proxy URL is wrong, such as an https:// scheme for a proxy that only speaks plain HTTP; or an environment variable (HTTPS_PROXY, ALL_PROXY, or system proxy settings) is silently sending your traffic through a proxy you did not intend. It is not a certificate problem, so changing verify will not help. Fix (best first): 1. Check the URL scheme and port. If the server is plain HTTP, use http:// (or put it behind TLS properly). If it should be HTTPS, confirm the port is the TLS port. 2. Check proxy settings. Requests reads http_proxy, https_proxy, no_proxy and all_proxy (upper case also works). Print them with: python -c "import urllib.request; print(urllib.request.getproxies())". Remember that the proxy URL scheme describes how you talk to the proxy, not the destination. Most HTTP proxies are used as http://proxyhost:port even for HTTPS destinations, which are tunnelled with CONNECT. urllib3's documentation notes that an https:// proxy URL for a proxy that only supports HTTP is a common cause of errors and should be changed to http://. 3. Remember that a proxies dict set on a Session can be overridden by environment proxies; pass proxies= on the individual request, or unset the stray variables, to test. 4. Test from the command line with curl -v against the same URL to see whether the server answers TLS or plain HTTP. 5. Do not set verify=False; it does not address this error and removes certificate checking. Verify: curl -v to the same URL shows a completed TLS handshake (or a plain HTTP exchange on an http:// URL), and requests.get(url, timeout=10) returns a response without SSLError. Sources: https://requests.readthedocs.io/en/latest/user/advanced/ https://urllib3.readthedocs.io/en/stable/advanced-usage.html