If you are experiencing an issue trying to purchase Remove Ads package, SMS or World Credits from the Add-Ons screen, please try the following:
1) Sign out of Fongo Mobile app (Account > Logout)
2) Sign out of iTunes account (iOS Settings > iTunes & App Store > Apple ID > Sign Out)
3) Restart phone (hold power button, swipe Power Off when it appears)
4) Open Fongo App and login
5) Attempt to make purchase, enter iTunes password when prompted