Issue
After a deploy to add the Heroku Metrics buildpack no dynos are showing on the app and seeing H14 errors
Resolution
This can happen if the app hasn't got a Procfile defined and the heroku/metrics buildpack was recently added.
The heroku/metrics buildpack needs to come first in the buildpack order, to allow the later buildpacks to set the "Default types for buildpack". This can be achieved by dragging the buildpacks settings page of the app to rearrange the order. Or through the CLI by removing the heroku/metrics buildpack and re-adding it with the --index 1 option: https://devcenter.heroku.com/articles/using-multiple-buildpacks-for-an-app#adding-a-buildpack
We'd also recommend adding a Procfile as to not rely on buildpack defaults.