File Attachments field query

Hello :),

Has anyone experienced an issue where if you include the physical path to the file like this in the File attachments field, it works perfectly: uploads/2023/01/filename.pdf

But if the exact same file location is held in a form variable ie [contact-download-file-attach] it does not attach? And I have 100% tested that if I include this variable in the form submit content, it outputs exactly right: uploads/2023/01/filename.pdf

Thanks so much :),
Tonya