Are you trying to access a LawStack subscription purchased previously, but on a new device?
Refresh the Subscription View In-App
First, refresh the subscription view in-app to ensure you are syncing down the latest info. You may do this in the app under Home > Updates Tab > Manage Subscription.
Is the Subscription View showing expired when you have previously purchased?
You may need to sign in to access your account details.
1) If you have a LawStack account, then you may simply sign in-app (via Settings > Account). Once signed in, refresh the Subscription view.
2) If you do not have a LawStack account and purchased via in-app purchase (and did not enter your email when you did), you may try verifying your original iTunes receipt in the app.