Why can't I open my iNotes anymore?

iNotes is saying that I need to pay for this app. I received no warning that this app was no longer going to be available. It was installed when I set up my phone a year ago.
The message I get now is "Sorry! You don't have paid for our app. of course, you can buy it now." With poorly written English like this, I'm wondering if this is a virus. Please help.

Apptest's iNotes is $2.99. Vittorio Calligaris' iNotes HD for Android (different app) is free.

Go to the Play Store, type inotes in the search box and see what's there. Those are about the only apps I see that claim to be able to read iNotes from an iPhone.