unknown column "_source_measurement" infuxdbv2.1

I'm using influxdb v2.1 and having this source measurement issue in task running. Someone please help.

    from(bucket: "volume_discount") 
    |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
    |> filter(fn: (r) => r["_measurement"] == "nginx_access_log")
    |> filter(fn: (r) => r["_field"] == "request")
    |> filter(fn: (r) => r["host"] == "volume-discount-process-server-1")
    |> count(column: "_value")
    |> group(columns: ["_time"])
    |> sum(column: "_value")
    |> map(fn: (r) => ({
    _time: now(),
    _field: "request",
    _measurement: "nginx_access_log", 
    _value: r._value 
 }))