How Post-back ID Works:
If you create template, you can use that template in bot settings button from dropdown.
In the top postback tab, that’s for if you use any child postback id in templates.
Otherwise templates can be selected from reply settings &
if you choose button or quick reply in that dropdown for postback type.
In postback template when you are creating a postback reply template, this postback will come during BOT settings in drop down menu if you select button type as postback.
And if you add any postback id as postback template’s child , You can set the reply of that postback id from BOT settings -> Postback top menu.
In Post-back Manager, When you’re creating post-back templates for post-back replies, you have to give unique postback id and child post-back id for each template.