It is, thanks!
You're currently testing the subscription purchase process using the App Store sandbox. This gives you a temporary free subscription that lasts 1 hour and renews a couple of times automatically before expiring. This is great for testing the purchase process; not so great for having access to premium features long-term.
To have reliable access to premium features in the Beta, I suggest you turn off the App Store setting on the bottom of this screen, and turn on the Subscribed setting on the screen. That should give you access to Premium which does not expire as the Apple sandbox expires your test subscription.