After downloading an app, you'll need to allow tracking when asked in order for your app download and activity to be credited to your FeaturePoints account.
After you download an app from the App Store, you may be asked to allow tracking like this:
Make sure you press "Allow" so that your download and activity is credited.
Never asked to allow tracking?
If you don't regularly see the above message after downloading apps, you may have disabled allowing apps to request to track. You can re-enable this by going to Settings → Privacy & Security → Tracking, then enable "Allow Apps to Request to Track".