Report Configuration - Unable to select "File_Upload" under Supporting Document

Report Configuration - Unable to select "File_Upload" under Supporting Document

Good day everyone. 

I encounter this issue whereby i have difficulty to select "File_Upload" under Supporting Document when i configuring my report.

Ps: I have create Supporting Document in Zoho creator form as subform and the add this "File Upload" inside this subform

This is to ensure the Attachement can be seen instead of "ID" number.