You are live! To send an SMS when a YouTube channel goes live using PHP and the YouTube API with Twilio, you need to create a folder named "Twilio-YouTube", install dependencies, store sensitive information in a `.env` file, connect to a PostgreSQL database, and write functions to check if the channel is live, save video IDs, send SMS notifications, and fetch subscribers' numbers. You can then test your code by running it from the console, create a cron job to run the code in intervals, and add a form on your website for subscribers to sign up. The complete code is available on Github.