Question with Message Filter Extension

Hi.

I created a Message Filter Extension target to filter spam sms messages, deferring the request to my backend. The extension makes the call and send this payload:

POST /server-endpoint HTTP/1.1
Accept: */*
Content-Type: application/json; charset=utf-8
Content-Length: 148
{
    "_version": 1,
    "query": {
        "sender": "14085550001",
        "message": {
            "text": "This is a message"
        }
    },
    "app": {
        "version": "1.1"
    }
}

My question is, is possible modify this payload to send the "receiver" number (is possible get the receiver number in this extension?), or use an identifier, to let my backend know which user number the filter was applied to.

I think is impossible because the extension makes the call and create the payload, and I don't see anything in docs to add other prop, but there's other way to know the "receiver" number of the sms?

Thanks:)