public DefaultBillingConnector(IBillingConnectorConfiguration configuration) : this(configuration, new RestClient(configuration.Url))
 {
 }
 public DefaultBillingConnector(IBillingConnectorConfiguration configuration, IRestClient client)
 {
     this.configuration = configuration;
     urlBuilder = new BillingUrlBuilder(configuration);
     this.client = client;
 }
 public BillingUrlBuilder(IBillingConnectorConfiguration configuration)
 {
     this.configuration = configuration;
 }