You've changed your mind on upgrading or downgrading your Heroku Postgres plan and now want to cancel the pending plan maintenance to stay on the original plan.
You can cancel the pending maintenance associated to the plan change via the CLI by running
heroku addons:upgrade or
heroku addons:downgrade and specifying the original add-on.
To do so, run:
heroku addons:upgrade <postgresql-addon-name> <original-plan>
heroku addons:upgrade postgresql-colorful-12345 standard-0 -a example-app