The slack sample template allows messaging to a slack channel or user. A slack app is required to use this template. The receiving slack workspace must download this app and authorize incoming webhooks. Slack provides a unique url for each channel/user to send a message. Copy and paste that url into the “API Endpoint” field in the template editor. Slack does not require authentication headers, so leave the auth fields blank.
For more information about the Slack API, visit: https://api.slack.com/incoming-webhooks.