Karabiner - Swap Cmd+Q and Alt+F4 - Partly functional

{
    "description": "Swaps Alt-F4 and Cmd-Q",
    "manipulators": [
        {
            "from": {
                "key_code": "q",
                "modifiers": {
                    "mandatory": [
                        "left_command"
                    ],
                    "optional": [
                        "any"
                    ]
                }
            },
            "to": [
                {
                    "key_code": "f4",
                    "modifiers": [
                        "left_alt"
                    ]
                }
            ],
            "type": "basic"
        },
        {
            "from": {
                "key_code": "f4",
                "modifiers": {
                    "mandatory": [
                        "left_alt"
                    ],
                    "optional": [
                        "any"
                    ]
                }
            },
            "to": [
                {
                    "key_code": "q",
                    "modifiers": [
                        "left_cmd"
                    ]
                }
            ],
            "type": "basic"
        }
    ]
}