Is there any way I can check if a certain user is subscribed to my channel, and how many months has he been subscribed using the helix API? I don’t mind if I need the user’s or broadcaster authorization.
Using the broadcasters authentication works best
You can’t see
You can capture this from chat notifications (and only if the user shares)
And is it possible to check it through the chat subscriber insight?
I don’t know to what you refer