When you first open Frank X app, Your Iphone totally freaks out. You can dismiss the UNTRUSTED ENTERPRISE DEVELOPER message but you can't open the app because your iphone is totally blown away by its awesomeness!
Tap Settings > General > Profiles or Profiles & Device Management. You then see a a profile for "Ons Interactive Solutions private limited" under the "Enterprise App" heading.
Tap the profile to establish trust for "Ons Interactive Solutions private limited"
You're then prompted to confirm your choice.
Note: An Internet connection is required to verify the app as well then a brain and at least one finger and one eye.