This is because the cache of the purchases in the Play Store isn't up to date. Here's how to update it:
- On your device navigate to Settings -> Apps -> All
- Find and tap on "Google Play Store"
- Tap on "Clear Cache"
- Restart your device
- Go back to the Play Store application, and log back in if prompted.
- Wait a bit in the play store app (1 minute, just to make sure the cache is rebuilt)
- Launch Infinite Flight