If the VyprVPN app doesn't see an account associated with your Apple email, then you may be prompted to purchase a subscription when you first open the VyprVPN app, even if you already have one outside of the Apple Store.
To get around this, select I have an account at the bottom. You will then be taken to the sign-in screen where you can sign into your existing account.
(Note: On some smaller phones, you may need to scroll down to see I have an account.)
If you need any further assistance, please contact our 24/7 Customer Success Team, who would be glad to assist.