app.json validation has been added

Change effective on 09 December 2021

We have published a change that enforces field validation around app.json for use on the Heroku platform.

The fields in the app.json are now required to be of the correct type. For example, the addons key must be of type Array and the environments values must be of type Object.

In addition, the only valid environments key names are "test" and "review".

For more information, see our page on app.json Schema.