You can request up to 100 promo codes for every version of each platform of your app, or for your in-app purchases.
App Promo Codes: Everything You Need To Know - Apptamin
Android Developers Blog: Create promo codes for your apps and in-app products in the Google Play Developer Console
Mobile App Privacy Policy Template & Examples
Set up offer codes - Manage subscriptions - App Store Connect - Help - Apple Developer
How to create, edit and delete offers in App Store Connect
App Store Connect Guide: How to release apps to the App Store, test with TestFlight, and more - Bitrise
App Store introduces 'Subscription Offer Codes.' Why does it matter?, by Denys Zhadanov
Request and manage promo codes - Offer promo codes - App Store Connect - Help - Apple Developer
Apple No Longer Accepting App Store Reviews for Redeemed Promo Codes - MacRumors
App Store Connect Guide: How to release apps to the App Store, test with TestFlight, and more - Bitrise
How to Find Online Coupon Codes
Set up promotional offers for auto-renewable subscriptions - Manage subscriptions - App Store Connect - Help - Apple Developer