Brand initiated messages, which need approval from WhatsApp, before being sent to users are HSMs or Post Session/ Notification Messages. These are template-based text messages, which can contain links, formatted texts (eg. bold, italics) and emojis. Once approved, we will also share the API details using which you can trigger the message by passing the user's phone number. You can read more about them here: 


https://support.morph.ai/portal/kb/articles/announce#How_to_create_Announcement


WhatsApp charges for each of these messages, the charges are different for different countries.