Slack: Posting to Webhook

From Slack, navigate Company Name→Administration→Manage Apps

Select "Custom Integrations"

Select "Incoming Webhooks"

Select a channel and copy the URL presented before saving the webhook.

Utilize the Slack Webhook in any Instant App with the following snippet:

function postToSlack(msg) {
   var payload = {
        "username": "BOTNAME",
        icon_url: "",
        text: msg
    };
	 var url = "https://hooks.slack.com/services/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";
   chatbox.buildCallExternalWebAPI("POST", url).value(payload);
}