I am not that familiar with Expression Engine and I want to know the best way to recieve and sendback response to the webhook sent to an endpoint I can setup in Expression Engine. Is it even possible? I tried writing code to recieve a POST request on a template I just created and testing a POST request results in a 403 error with "The form is expired. Please refresh and try again."
Sounds like you'll need to create a plugin or module, which lets you create a corresponding Action URL you can POST to, and in the plugin/module code you can receive the POST request and do what you want with it.
https://docs.expressionengine.com/latest/development/models/action.html https://docs.expressionengine.com/latest/development/modules.html
If you upgrade to EE6 there is a built in CLI tool to generate the base add-on files to get you started.