Facebook restricts proactive messaging for Marketing and Sales use cases. However, they allow sending proactive messages for a support use case such as as order confirmation, booking confirmation, delivery updates, etc.
For this a message template approval is required from Facebook (https://developers.facebook.com/docs/whatsapp/message-templates/). We will help you throughout this process.
Additional pricing will be applicable for proactive messages.
For more details, contact firstname.lastname@example.org.