I'm trying to sent my customers a receipt through Facebook Messenger. They have already logged in to my website using Facebook oAuth2.
I can get their name, email, pictures, id and some other stuff. But in order to initiate a conversation it seems like I need their PSID - which you can only get after a user has messaged me first.
But I've seen other companies sent receipts through Messenger without the customer having to initate the conversation. How can I do this?