SSRS report filepath parameters

I'm trying to migrate reports over to a new SSRS 2019 server and one particular report gets called from an excel macro where it reads in the contents of a file located at a given filepath. I've tried the methods of defining the report path as described on the Microsoft site which is

http://server/ReportServer?/foldername/reportname¶metername= "filepath"

I've tried sever different ways to pass the file url in as a parameter but every time it comes up as an error >path of the item is not valid. The file exists on a network server and if I run the report manually from the report sever I can just pass in the network url as follows "\\\\\filename.txt" and it works as expected. When I try to run this by passing in the filepath into the url and running from a browser it tells my invalid path. Long story short, how do you pass in a network server filepath that is not local to the report server as a param?