In an extension there is no “event” beyond
window.Twitch.ext.viewer.onChanged
Which only tells you the data has changed so then you call the subscriptionStatus object
And the docs are pretty clear on what the sub data is
window.Twitch.ext.viewer.subscriptionStatus
null
or
{tier:1000}
or 2000/3000
So not sure what “events” you are after when in the context of an Extension?