$HOME/.config/notify/provider-config.yaml.
Each provider (slack, discord, etc.) is specified at the top level by name, and then can have 1 to many configurations for that provider identifed by a unique id field.
Slack
Fields:slack_channel: The Slack channel to post toslack_username: The name of the bot to post asslack_format: By default just{{data}}but you can specify more formattiong detailsslack_webhook_url: The URL for the Slack integration webhook (See Slack help for more information)