Adding an attachment to a service bill fails

[AndrasFromTransAxHealthCare]

Using the following code, adding an attachment to a service bill fails with a 404 not found error.

        BillAttachmentData billAttachmentData = new BillAttachmentData();
        billAttachmentData.OriginalFileName = "test.pdf";
        billAttachmentData.FileBase64Content = Convert.ToBase64String(attachment);

        BillAttachmentWrapper billAttachmentWrapper = new BillAttachmentWrapper();
        billAttachmentWrapper.Attachments = new List<BillAttachmentData>();
        billAttachmentWrapper.Attachments.Add(billAttachmentData);
        BillAttachmentWrapper returnedData = serviceBillAttachmentService.InsertEx(CompanyFile, transaction.UID, billAttachmentWrapper, Credentials);