JSSheet parsing from a File Attachment field with an xlsx file

I'm working on a function where users upload a xlsx file into a File Attachment field, and through JavaScript and JSSheets, we're then able to map the files into another table and populate fields which field names are the same as the columns of the table...

My first issue, is that I don't think I have the actual URL of my first test file (which I've uploaded into a QB app) so that the JavaScript is actually looking at the content.

Current link to the file attachment is as follows:

https://<domain>.quickbase.com /up/<dbid>/g/rb/eg/va/<filename>.xlsx