Manual Steps¶
This documentation includes a set of steps that do not have an automated CLI command, and must be performed manually in the UI. They are formatted as a list of QA-like problems and solutions.
Mattermost In/Outgoing Webhooks¶
Typical users cannot create incoming or outgoing webhooks in Mattermost. Instead of enabling this for all, create them and share the information to the group. These steps are not rocket science, but I've included images since this information might be informative for the participants as well.

Webhooks are added in the Integrations > Incoming Webhooks section of the Mattermost System Console.

There are not too many settings in the menu. Choose title, description, channel, and username that it will be posted as. The username can also be later on changed in the workflow using the username field in the JSON body of the webhook.

The URL shown here should be kept secret. Sending anything to that URI will post a message to the Mattermost channel.
Sending an HTTP POST request to that URL with a JSON body containing text field will post the content of that field as a message to the Mattermost channel. For example:

A command line tool curl has been used to send a POST request to the URL seen in the screenshot above.

The command appears in the Mattermost Town Square channel as a message. Note that anyone could've sent this message.
You can read more about this feature at Mattermost's Incoming Webhooks documentation.
Mattermost incoming custom username forbidden¶
To change the incoming username, the field is username instead of user_name, AND the following setting must be enabled from the Mattermost System Console > Integrations > Integration Management:
Enable integrations to override usernames: True