I am trying to make chat functionality work for an extension I’m designing, but unfortunately I receive an error whenever the function is called:
HTTP505: VERSION NOT SUPPORTED - The server does not support, or refuses to support, the HTTP protocol version that was used in the request message.
(Fetch)GET - https://<CLIENT_ID>.ext-twitch.tv/<CLIENT_ID>/<VERSION_NUMBER>/<UNKNOWN_VALUE>/[object%20Object]
I don’t believe the pinned endpoint was ever official supported. The article you linked is an RFC, an announcement of what the plans/thoughts are at the time but doesn’t guarantee any of that will make it to the finished product, or without changes.
If you want to know what endpoints are supported and their requirements for use, refer to the docs as that is the definitive source of supported endpoints, not the forums.