For reference, this will work in the desktop version's send tab since the same to a "paytomany.csv" format contents. (automatically toggles 'paytomany' options)
However, QML GUI Electrum doesn't have the option to paytomany so it will not accept it.

If you want that feature, consider posting a "feature request" issue in GitHub: https://github.com/spesmilo/electrum/issues
There doesn't seem any previous request to add it.