code: func NewClient(apiKey, apiSecret string) (*Client, error) {
  	if apiKey == "" {
  		return nil, errors.New("apiKey can not be empty")
  	} else if apiSecret == "" {
  		return nil, errors.New("apiSecret can not be empty")
  	}
  
  	c := &Client{
  		apiKey:    apiKey,
  		apiSecret: apiSecret,
  		useOauth:  false,
  	}
  
  	c.Account = &Account{c}
  	c.SMS = &SMS{c}
  	c.USSD = &USSD{c}
  	c.Verify = &Verification{c}
  	c.HTTPClient = http.DefaultClient
  	return c, nil
  }
docs: // NewClient creates a new Client type with the
  // provided API key / API secret.