Slack (https://slack.com) is a real-time messaging tool which Message Blocks can integrate with to receive notifications about your Message Blocks registration. If you have an active Slack account you can integrate with Message Blocks following the instructions below.
In Slack open your profile and go to Apps & Integrations to open the App Directory. Choose "Manage" in the top right corner, and then "Custom Integrations" and select "Incoming WebHooks". If you do not see "Incoming WebHooks" as an option, you should search for it in the search bar at the top of the page. Under the WebHook logo click "Add Configuration".
In the drop-down choose the channel you want Slack to post to, and click the green "Add Incoming WebHooks integration" button.
Copy the Webhook URL in redtext and go to your Message Blocks event. Go to Registration Settings, under Registration Notifications and paste the link in Slack Integration URL.