I would like to use Redis Notification feature, but I get an error message "(error) ERR unknown command 'config'".
You can enable and config Redis to use keyspace notifications via the CLI. For example,
heroku redis:keyspace-notifications REDIS_URL -c 'AKE' -a your-app-name
where the string following
-c is used to set the config options. In the above example,
'AKE' means enabling keyspace notifications for all events except for key miss events.
You can run
heroku redis:keyspace-notifications --help to see descriptions of all the config options. These are the same config options as shown in the official open-source Redis docs. See Heroku CLI Commands for more info.