public async Task ApiKeyNotFound()
        {
            var apiClient = new PrivateApi("xxxxxxxxxxx", "xxxxxxxxxxx");

            try
            {
                await apiClient.GetPermissions();
            }
            catch (BitFlyerApiException ex)
            {
                Assert.Equal(ex.ErrorResponse.Status, -500);
                Assert.Equal("Key not found", ex.ErrorResponse.ErrorMessage);
            }
        }
        public async Task GetPermissions()
        {
            var res1 = await apiClient.GetPermissions();

            Assert.NotNull(res1);
        }