Unrecognizable lambda output Cognito on pre token generation trigger

I am using the pre token generation trigger to insert custom claims to my token. One of the claims is a list:

exports.handler = (event, context, callback) => {
event.response = {
    "claimsOverrideDetails": {
        "claimsToAddOrOverride": {
            "subscription_name": "FLEXI",
            "subscriptions" : {
                "id": "Wakanda",
                "country": "Namibia"
            }
        },
        "claimsToSuppress": ["token_use"]
    }
};


callback(null, event);

}

What am I doing wrong?