Alright, first things first, let's get that Slack App up and running. Head over to the Slack API dashboard (https://api.slack.com/apps) and hit ‘Create New App’. Give your app a name and pick the Slack workspace where you want those notifications to land. Once your app is created, you'll get a 'Client ID' and 'Client Secret'. Keep those handy, you'll need them later.

Next, on your Slack app page, find 'Incoming Webhooks' in the features list on the left. Flip the switch to 'Activate Incoming Webhooks', then click 'Add New Webhook to Workspace'. Choose the channel for your notifications, and voilà, you'll get a Webhook URL.

Now, let's hop over to the Supabase dashboard (https://app.supabase.io/) and create a new project. Just give it a name and click 'Create New Project'. Easy peasy.

In your shiny new project, go to the 'SQL' tab and click 'New Query'. Here’s where the magic happens. Write a function that grabs the data you want to trigger a Slack notification. This function will send an HTTP POST request to your Slack Webhook URL with a JSON payload containing your message.

To create a function, use the CREATE OR REPLACE FUNCTION SQL command. For sending the HTTP request, use http.post() within the function.

Now, head to the 'Table Editor' tab and pick the table you want to keep an eye on. Go to the 'Triggers' tab and click 'New Trigger'. Specify the actions (INSERT, UPDATE, DELETE) that should fire the trigger, and select the function you wrote in step 4 as the procedure to run.

Hit 'Save', and now, whenever the specified action happens on your table, a notification will be sent to your Slack workspace.

Time to see if everything's working! Perform the action that should trigger the notification. Check the Slack channel you set up to see if the notification pops up.

If something's off or you don't see the notification, double-check your setup in both Supabase and Slack. You might need to debug your function or review your Slack App settings if things aren't going as planned.