Slack setup

Create a Slack app if you don't have one already
Pick a name, choose a workspace to associate your app with, and then click Create App
Select the Incoming Webhooks feature and click the Activate Incoming Webhooks toggle to switch it on
Click Add New Webhook to Workspace
Pick the channel the app will post to and then click to Authorize your app
You should see a new entry under the Webhook URLs for Your Workspace section

See the Slack API docs for more detailed instructions on creating Slack apps.

Set environment variables in .env
- Set ENABLE_SLACK_POSTING to true
- Set SLACK_WEBHOOK_URL to the Webhook URL from your Slack app setting