Get Active Extension Version info
In order to send a chat message via https://dev.twitch.tv/docs/extensions/reference/#send-extension-chat-message you need to know the current active version of your extension. There's no way to retrieve information about your extensions' versions.
There's one way which is kind of roundabout, by first using /extensions/${CLIENT_ID}/live_activated_channels
to get a list of users, then using /helix/users/extensions/list
on one to find the extension again and get its version there.
This could be much quicker to find if live_activated_channels
had a version
field with the live extension version (it only ever returns a list of channels using the live version).
There could also be a /extensions/${CLIENT_ID}/versions
endpoint which would list each version and have information about each, much like the dev dashboard Versions page.