Iterate through folders

Sure, the basic premise involves a recursive script that calls itself over and over again:

on run
set theFolder to (choose folder with prompt "Select the start folder")
doSomethingWith(theFolder)
end run

on doSomethingWith(aFolder)
tell application "Finder"
set subFolders to every folder of aFolder
repeat with eachFolder in subFolders
my doSomethingWith(eachFolder)
end repeat
end tell
-- rest of code to deal with the folder goes here
end doSomethingWith

So you start off at one folder chosen via choose folder. The doSomethingWith() handler then looks for every folder inside that folder and for each one, calls itself. In this way you don't need to know the name of the folder, or the depth - you'll just keep iterating through all the folders.

Where did I go wrong?

Where you went wrong is that you haven't been using AppleScript for 10 years or more 🙂

Seriously, historically Mac paths are based on colon-delimited paths, not the UNIX-based /-delimited paths. Therefore your mistake is in how you're defining the starting path. Apple have done some work in streamlining the process and making them interchangeable, but there are still gotchas, like the one you encountered.

You should find either of these work fine:

set theFolder to ":Volumes:media:content" as alias
set theFolder to "media:content" as alias