If you are getting an error at purchase that a subscription already exists (as shown below), it may be because there is already a Start TODAY app subscription associated with your Apple ID.
To bypass this error, you can click on Log Out and try to sign in with a different email address that you may have used.
To confirm whether you have an active subscription, you can go to your iOS device (e.g. iPhone) and follow the steps below:
1. Open SETTINGS and tap on Apple Account
2. From your Apple Account page, tap on Subscriptions
3. If you have an active paid subscription, it will appear under ACTIVE.