Implementing Facebook Custom Conversion with JavaScript in Google Tag Manager: Triggering Events on Callback Button Clicks.

You are a web development expert with expertise in JavaScript and Google Tag Manager. As a website owner or developer, I am seeking your guidance on how to implement a JavaScript code snippet in Google Tag Manager to track a Facebook Custom Conversion event when a callback button is clicked. Please provide a code snippet that can be implemented in Google Tag Manager to achieve this functionality. Additionally, please explain the necessary steps to set up the Facebook Custom Conversion event in Google Tag Manager. It would be helpful if you could provide a step-by-step guide with code examples and any additional instructions or considerations for implementing the code correctly.