Read a parameter from URL

I am using flux script in Grafana 8.0.6 and InfluxDB2.0 as my Datasource

Dashboard URL:

using following fluxcscript I try to read the url parameter “var_instance” as follows

from(bucket: “ICEIPABucket”)
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r["_measurement"] == “java_os”)
|> filter(fn: (r) => r["_field"] == “SystemCpuLoad”)
|> filter(fn: (r) => r[“host”] == “myz-x2-bexyz-01”)
|> filter(fn: (r) => r[“instance_address”] == ${var_instance})
|> aggregateWindow(every: v.windowPeriod, fn: mean, createEmpty: false)
|> yield(name: “mean”)

But, I am getting error “Invalid Token for primary expression” at line 6 while using ${var_instance}

Can you please help me how to read parameter from the URL, following snapshot will cover the same details about this issue.

This is to communicate data from one cell of Dashboard to another cell using parameters in the URL