WaitTaskAsync throws JSON deserialisation error when task is processing

[ileeder-iit]

We are running a basic PDF-DOCX conversion using the .NET SDK. This had worked for us previously, and has recently started failing (unfortunately aligning with our production go-live). It could also be related to the production server having higher capacity, and running faster.

This is our basic job structure:

var job = await _cloudConvertClient.CreateJobAsync(new JobCreateRequest
{
    Tasks = new
    {
        upload_pdf = new ImportUploadCreateRequest(),
        convert = new ConvertCreateRequest()
        {
            Input = UploadTaskName,
            Input_Format = "pdf",
            Output_Format = "docx",
        },
        export_it = new ExportUrlCreateRequest()
        {
            Input = ConvertTaskName
        }
    }
});

We upload the PDF, wait for that to complete and check for success status. Then we wait for conversion job to complete:

Response<TaskResponse>? conversionResult;
do
{
    conversionResult = await _cloudConvertClient.WaitTaskAsync(conversionTask!.Id);
}
while (conversionResult.Data.Status == TaskStatus.processing || conversionResult.Data.Status == TaskStatus.waiting);

At this point we get a deserialisation error:

2026-05-07T11:30:15.3820567Z       An error occurred while downloading report with ID 15300
2026-05-07T11:30:15.3820631Z       System.Text.Json.JsonException: The JSON value could not be converted to System.Nullable`1[System.Int32]. Path: $.data.credits | LineNumber: 0 | BytePositionInLine: 151.
2026-05-07T11:30:15.3820676Z        ---> System.InvalidOperationException: Cannot get the value of a token type 'String' as a number.
2026-05-07T11:30:15.3820724Z          at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_ExpectedNumber(JsonTokenType tokenType)
2026-05-07T11:30:15.3820766Z          at System.Text.Json.Serialization.Converters.Int32Converter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)
2026-05-07T11:30:15.3820833Z          at System.Text.Json.Serialization.Converters.NullableConverter`1.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)
2026-05-07T11:30:15.3820881Z          at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
2026-05-07T11:30:15.3820928Z          at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
2026-05-07T11:30:15.3820977Z          at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
2026-05-07T11:30:15.3821572Z          at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
2026-05-07T11:30:15.3821645Z          at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
2026-05-07T11:30:15.3821695Z          at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
2026-05-07T11:30:15.3821771Z          --- End of inner exception stack trace ---
2026-05-07T11:30:15.3821848Z          at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)
2026-05-07T11:30:15.3821898Z          at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
2026-05-07T11:30:15.3822008Z          at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 json, JsonTypeInfo`1 jsonTypeInfo)
2026-05-07T11:30:15.3822054Z          at CloudConvert.API.RestHelper.RequestAsync[T](HttpRequestMessage request, CancellationToken cancellationToken)

I can't find a way to view the raw JSON, but it looks like the credits field is coming back as a string (possibly empty string '') that can't be deserialised to a nullable integer int?.

But this is only an issue while the task is processing. If we introduce an artificial 10s delay before checking the conversion task, it succeeds every time.