Why are `heroku pg` commands failing with "Couldn't find that add on"?

Resolution

This message gets shown when the CLI can't verify you have access to these two resources, usually because the parameters being used to identify the database(s) are somehow ambiguous.

Instead of using DATABASE_URL for example, you could try looking up the color URL using heroku pg:info (this will be something like HEROKU_POSTGRESQL_TEAL_URL) or the addon name using heroku addons (this will be something like flowing-example-1234). Using one of these more specific identifiers should help to resolve any issues in running the command.