We use Citrix ShareFile for secure file uploads. You can read about their security measures here: https://www.sharefile.com/resources/citrix-sharefile-security-and-compliance-frequently-asked-questions.
When you have clicked on the upload button and the files have finished uploading, you should see the word "Uploaded" in green next to your file name. If you do not see "Uploaded" next to the file name, please upload again. If you are having issues getting your file to upload, please contact the recipient you are sending the files to for assistance.