This article provides the details on how, through the use of the Loyalty feature, it is possible to give an introductory reward to subscribers who download your App.
To create introductory rewards to subscribers who download your App, we recommend going with the Loyalty feature.
To do so you can create a Loyalty that offers a free code and then turn on the "Push Notes Award" as shown in the screenshot in the link below
(Click on the image to enlarge.)
Note: this will only reward users who download the app and launch it for the first time.