If you have started a trial period, you can easily upgrade to a lifetime subscription.
You need to cancel your current trial first.
Go to App in the Air → Profile → Settings → Manage Subscriptions → there you will be redirected to the iTunes app. Select App in the Air and click Cancel.
Then go to App in the Air Settings → click on your subscription button at the top of the screen and purchase Lifetime.
Go to the Play Store app → left menu → Subscriptions → select App in the Air → unsubscribe.
Then go to App in the Air → Profile → Settings → Manage Subscriptions → purchase Lifetime.
If you have already purchased an annual subscription and want to change it to a lifetime subscription, contact our support team via the feedback option in the app settings.