Register a connected WhatsApp number on the Cloud API

Re-runs Meta's Cloud API registration for a WhatsApp account that is already connected. Use it when the number has its own two-step verification PIN: the connect flows register with a default PIN, Meta rejects that with error 133005, and the number then fails every send with the misleading '(#200) You do not have the necessary permission to send messages' while the account still shows as connected. The PIN is used for this call only and is not stored.