ExternalData and local paths

Usage
1

I’m trying to add a local path to ExternalData_URL_TEMPLATES like so:

set (ExternalData_URL_TEMPLATES "file:///Users/benvining/Documents/MTM/audio-samples/%(algo)/%(hash)")

and my build keeps failing with:

-- Fetching "file:///Users/benvining/Documents/MTM/audio-samples/MD5/2e7eef9d4b1f9e6f7a7957f276248c4d"
CMake Error at /Users/benvining/.asdf/installs/cmake/3.28.0/share/cmake-3.28/Modules/ExternalData.cmake:1181 (message):
  

  Object MD5=2e7eef9d4b1f9e6f7a7957f276248c4d not found at:

    file:///Users/benvining/Documents/MTM/audio-samples/MD5/2e7eef9d4b1f9e6f7a7957f276248c4d ("Couldn't read a file:// file")

Even though that file does exist at that local path.
Any ideas?