Apple now allows to create custom offer codes

Apple now allows developers to create custom offer codes of their choice.

Now it's even easier to acquire, retain, and win back subscribers. In addition to one-time-use codes, you can now create custom codes in App Store Connect — each with a unique name that you choose (such as SPRINGPROMO). Each code can be redeemed through a direct URL or within your app.

Apple Developer

Apple Developer: Custom offer codes for subscriptions now available