code: func NewClient(customerNumber string, apiKey string, apiPassword string) (*Client, error) {
  	if customerNumber == "" || apiKey == "" || apiPassword == "" {
  		return nil, fmt.Errorf("credentials missing")
  	}
  
  	return &Client{
  		customerNumber: customerNumber,
  		apiKey:         apiKey,
  		apiPassword:    apiPassword,
  		BaseURL:        defaultBaseURL,
  		HTTPClient: &http.Client{
  			Timeout: 10 * time.Second,
  		},
  	}, nil
  }
docs: // NewClient creates a netcup DNS client