The Lightstream Integration beta is currently limited to Mixer partners and pro subscribers.
This past June, a large number of free 3-month Pro subscriptions were issued to anyone who logged into Mixer between May 24th and May 28th. If you previously had access and can no longer use the integration, it’s likely that your free Pro subscription recently expired.
If you were already a Pro subscriber prior to receiving the free months, it’s possible that the giveaway turned off the auto-renew option on your account and you will need to resubscribe.
You can instantly restore your Integration access by renewing your Mixer Pro subscription at https://mixer.com/pro