Publication URL declaration in the Facebook client chat plug-in

How to designate the publishing URL for the Facebook Customer Chat plug-in?

https://developers.facebook.com/docs/messenger-platform/discovery/customer-chat-plugin/

In the Message Type and Template Support section, they indicate support for Postback. Further down the page, they refer to an optional event called "messaging_postbacks" and "messaging_referrals". Do I declare these attributes as attributes of the div fb-customerchat tag?

Here is my code:

I have a simple script that looks for php: // input and records the data sent, but I do not receive any data.