The $delete event does not work

[vking34]

Here is my engine configuration:

{
    "engineId": "2",
    "engineFactory": "com.actionml.engines.ur.UREngine",
    "sparkConf": {
        "master": "local",
        "spark.serializer": "org.apache.spark.serializer.KryoSerializer",
        "spark.kryo.registrator": "org.apache.mahout.sparkbindings.io.MahoutKryoRegistrator",
        "spark.kryo.referenceTracking": "false",
        "spark.kryoserializer.buffer": "300m",
        "spark.executor.memory": "4g",
        "spark.driver.memory": "3g",
        "spark.es.index.auto.create": "true",
        "spark.es.nodes": "elasticsearch",
        "spark.es.nodes.wan.only": "true"
    },
    "algorithm": {
        "indicators": [{
                "name": "view"
            },
            {
                "name": "buy"
            },
            {
                "name": "add-to-cart"
            },
            {
                "name": "rating"
            }
        ]
    }
}

According to the Universal Recommender document, to delete item, we use $delete event.
https://actionml.com/docs/h_ur_input#delete-items
However, I tried to use the $delete event:

{
    "event": "$delete",
    "entityType": "item",
    "entityId": "3453",
    "eventTime": "2021-01-14T00:39:45.618Z"
}

However, when I query, the item still remains in the result. It seems not working.