Why am I seeing `certs:auto:disable is not a heroku command.`?

Issue

When trying to disable Automatic Certificate Management (ACM) with heroku certs:auto:disable I see the error certs:auto:disable is not a heroku command.

Resolution

This error message is shown when using outdated versions of the Heroku Command Line tools. Download and install the latest version to fix this using the instruction here https://devcenter.heroku.com/articles/heroku-cli

For users who are still having trouble, please check to see if you have the legacy heroku gem installed and follow the steps here https://devcenter.heroku.com/articles/heroku-cli#uninstalling-the-legacy-heroku-gem to remove it.