Sends an approved template into a conversation that already runs on WhatsApp. This is the only way to write
into a WhatsApp conversation through the API: POST /v2/conversations/{conversation_id}/messages rejects
WhatsApp conversations with conversation_channel_not_supported. A template also reopens the 24 hour
customer service window when the contact has been silent, which plain messages cannot do.

The conversation must be a WhatsApp conversation and must not be frozen. The template must belong to the
same WhatsApp Business Account (WABA) as the number of the conversation, and must be text-only.

account_id is the account the template is sent as, recorded as the author of the message in the Customerly
inbox. It defaults to the account owning the access token. The assignee of the conversation is left untouched.

Example request

{
  "whatsapp_template_id": 42,
  "parameters": {
    "name": "John",
    "order_id": "A-19822"
  }
}