code: func NewClient(httpCl HTTPClientInterface, smtpCl SMTPClientInterface, baseURL ...string) *Client {
  
  	client := &Client{
  		httpClient: httpCl,
  		smtpClient: smtpCl,
  		apiBase:    apiBase,
  	}
  
  	if len(baseURL) > 0 {
  		client.apiBase = baseURL[0]
  	}
  	return client
  }
docs: // NewClient function