public async Task SubscribeAsync_FailsOnRelativeReceiverAddress()
        {
            // Arrange
            Initialize(TestId);
            Uri relative = new Uri("relative", UriKind.Relative);

            // Act
            ArgumentException ex = await Assert.ThrowsAsync <ArgumentException>(() => _client.SubscribeAsync(TestId, relative));

            // Assert
            Assert.Contains("The URI for where Instagram will send WebHook requests must be an absolute URI. By default this should be of the form 'https://<host>/api/webhooks/incoming/instagram'.", ex.Message);
        }