Applications fail to build on the new
heroku-18 stack (https://devcenter.heroku.com/articles/heroku-18-stack).
Your application may fail to build on the new
heroku-18 stack because your app is incompatible, due to changes in packages available in the stack, as well as available language runtimes.
In order to change stacks, please use
heroku stack:set (https://devcenter.heroku.com/articles/upgrading-to-the-latest-stack), specifying the previous stack you were using (either
heroku-16), and deploy a new release.