Heroku-16 stack has reached end-of-life
Change effective on 01 May 2021
Apps using the Heroku-16 stack will continue to run, but will no longer receive security updates, so should be upgraded to a more recent stack as soon as possible.
From May 3rd, 2021, it will no longer be possible to create new Heroku-16 apps. Review App and Heroku CI functionality will be unaffected.
From June 1st, 2021, builds will no longer be allowed for any Heroku-16 apps, including those used by Review Apps and Heroku CI. All other non-build functionality will continue to work, and existing apps will continue to run.
See the Heroku-16 End-of-Life FAQ for more information.