How To Request for One-Time Notification For Your Facebook Page
With Facebook's recent changes, pages can only send promotional messages to users within 24-hour from the user messaging the page and after that you can't send any promotional messages unless the user give you a permission by requesting them to allow you to send a One-Time Notification after 24 hours.
In order to send One-Time Notification, you must first request from Facebook to allow your page to request OTN from users.
In this tutorial, we'll show you how to request OTN for your Facebook page.