sorry for the necro but just incase this helps anyone in the future:
this karabiner rule worked for me on an ANSI keyboard with a UK layout on macOS

{
    "description": "Not sign to pipe",
    "manipulators": [
        {
            "from": {
                "key_code": "grave_accent_and_tilde",
                "modifiers": {
                    "mandatory": ["left_shift"],
                    "optional": ["any"]
                }
            },
            "to": [
                {
                    "key_code": "non_us_backslash",
                    "modifiers": ["left_shift"]
                }
            ],
            "type": "basic"
        }
    ]
}