Add a number
Open Automation → Numbers. Paste Phone Number ID, WABA ID, and access token from Meta Developer.
Webhook
Copy the webhook URL and verify token into your Meta app. Subscribe to messages. Send a test inbound message; it should appear in the inbox.
Templates
After the number is live, sync templates so broadcasts can pick an approved message.
Sandbox vs production
Keep test numbers on a staging workspace. Production tokens should belong to a system user with only the permissions you need.