I had the following problem when trying to install a camera plugin on IONIC 3 , not just the camera plugin, but it gives a similar error when trying to install other plugins .
cordova plugin add cordova-plugin-camera --save
Error: Failed to fetch plugin [email protected] via registry.
Probably this is either a connection problem, or plugin spec is incorrect.
Check your connection and plugin name/version/URL.
Error: cmd: Command failed with exit code ENOENT
[ERROR] An error occurred while running cordova plugin add cordova-plugin-camera --save (exit code 1).