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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";
platform.buildCallExternalWebAPI("POST", url).value(payload);
}