How can I pass the following cmd line command using system.callSystem() method?

In some cases the path that you have in your own commad prompt window is different than what system.callSystem() has.  Do you get different outputs when you run something like "echo %PATH%" from the command promo and from running it in system.callSystem() method?

Also note that the "curl" command is not, by default part of Windows installation.  Even though you have it on your machine, an end user may not have it.  You should use the absolute path to the executable if you know where it will exist on the end-user's machine.  "curl" is by default on all macOS installations so you can definitely use it there.  I strongly do not recommend ExtendScript sockets as they do not support SSL and it is quite slow.

hope this helps!

Does it help to put the entire command in quotes?

var curlCmd = 'cmd.exe /c "curl https://raw.githubusercontent.com/adiraimaji/checkforupdate/master/checkforupdate.json > %USERPROFILE%\Desktop\Testfile.json"';

Running cmd requires elevated user privileges, so this is bound to fail a majority of times for regular users, anyway. You need to create an actual socket connection in Extendscript itself and check for a manifest.xml or whatever you intend to use to handle your versioning.

Mylenium