Based on an error message, adding a platform is not performed due to a lack of permissions
Command failed with exit code EACCES
when trying to create a folder /media/denny/New Volume/projects/mobile/tester/platforms/android/cordova/version.
If you are using a Mac, you should see this answer by holmescn.
If you are using Linux, try running
chmod -r 777 *
in your root projects to get enough permissions.