code: func CreateMessage(c *messagebird.Client, conversationID string, req *MessageCreateRequest) (*Message, error) {
  	uri := fmt.Sprintf("%s/%s/%s", path, conversationID, messagesPath)
  
  	message := &Message{}
  	if err := request(c, message, http.MethodPost, uri, req); err != nil {
  		return nil, err
  	}
  
  	return message, nil
  }
docs: // CreateMessage sends a new message to the specified conversation. To create a
  // new conversation and send an initial message, use conversation.Start().