code: func Start(c *messagebird.Client, req *StartRequest) (*Conversation, error) {
  	conv := &Conversation{}
  	if err := request(c, conv, http.MethodPost, path+"/start", req); err != nil {
  		return nil, err
  	}
  
  	return conv, nil
  }
docs: // Start creates a conversation by sending an initial message. If an active
  // conversation exists for the recipient, it is resumed.