Most likely SAP isn't able to access the file and hence passing value as -1.
Looking at the file path, you are using Citrix, and it's client has file access restrictions.
Try to upload the file using the same path, using GUI_UPLOAD, and check if you are able to upload the file using Citrix. If no, then it is related to access issues.
Also, to confirm the finding, check if the method works correctly for a local file.
Thanks, Juwin