Raymond,
According to the documentation found here:
https://developer.docuware.com/sdk/platform-eagle/html/57da87ed-111c-4f78-96e9-75d3b9462ce9.htm
and
https://developer.docuware.com/sdk/platform-eagle/html/c3431d10-b73e-4b98-814a-a0d235d21f80.htm
there are two different upload methods you can use, and one is meant for larger files.
Here is C# code I use to upload files, and I set the threshold at 10 MB:
 
        public static Document UploadFileToFileCabinet(FileCabinet fileCabinet, string uploadFile, Document indexInfo = null)
        {
            LastError = "";
            try
            {
                // We will use a standard upload method for smaller files, but the "Easy" version for larger files, otherwise
                // large file uploads might fail (the "Easy" version is meant for huge file uploads, according to the documentation).
                int largeFileThresholdInBytes = 10 * 1024 * 1024;    // 10 MB
                Document uploadedDoc = null;
                FileInfo fileInfo = new FileInfo(uploadFile);
                if (fileInfo.Length < largeFileThresholdInBytes)
                {
                    // Smaller file.
                    uploadedDoc = fileCabinet.UploadDocument(indexInfo, fileInfo);
                }
                else
                {
                    // Larger file.
                    uploadedDoc = fileCabinet.EasyUploadSingleDocument(fileInfo, indexInfo);
                }
                return uploadedDoc;
            }
            catch (Exception ex)
            {
                LastError = ex.Message;
                return null;
            }
        }
The "Easy" method is part of some extensions, though, so I am not sure it has a direct resource end-point when doing API calls via non-NET environments.
Are you using .NET to access the API? If not, what are you using? I see in my non-NET code (Visual FoxPro) that if I need to upload a large file I shell out to the .NET program I wrote to upload files instead of using the straight HTTP endpoint to upload. So, I must have run into the same issue you are facing. The only truly reliable way to upload huge files is with the .NET code. With that code I have uploaded files greater than 1 GB in size.
Thanks,
Joe Kaufman