You also need to register the phone number first. The API is defined https://developers.facebook.com/docs/whatsapp/cloud-api/reference/registration/:

curl 'https://graph.facebook.com/v22.0/<phone-fbid>/register ' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer <token>' \
-d '
{
  "messaging_product": "whatsapp",
  "pin": "<6-digit-pin>"
}