Here are the steps to subscribe to AirBrush Premium:
1. Open AirBrush, tap AirBrush Premium on "Home" as below, choose your preferred plan and continue.
2. Open AirBrush, tap 'Settings' on the top right corner, then tap AirBrush Premium, choose your preferred plan, and continue.
If you fail to purchase, please follow the steps:
1. Make sure you downloaded the app from the App Store or Google Play Store, rather than any third-party sources.
2. To resolve payment issues, please refer to What Payment Method Can I Use to Subscribe?
3. You may also check if you have disabled In-app Purchases on your phone with the following steps:
Settings >> Screen Time >> Content & Privacy Restrictions >> iTunes & App Store Purchases >> In-app Purchases (please set it to Allow)