Support of Variables for Native Mongo Queries in Metabase

I want to add a variable to the given MongoDB query in Metabase. I know that it is supported after https://github.com/metabase/metabase/issues/3653 I have given my query below which is not working with the variable.

My query is:

[
  {
    "$project": {
      "lastCommGenTS": "$lastCommGenTS",
      "lastUpdated": "$lastUpdated",
      "extBatMvLow": "$extBatMvLow",
      "regNo": "$truckRegNo",
      "derivedStatus": "$derivedStatus"
    }
  },
  {
    "$match": {
      "$expr": {
        "$and": [
          {
            "$eq": [
              "$regNo",{{regNo}}
            ]
          }
        ]
      }
    }
  },
  {
    "$project": {
      "_id": "$_id",
      "regNo": "$regNo",
      "derivedStatus": "$derivedStatus",
      "lastcommtimeIST": {
        "$dateToString": {
          "format": "%Y-%m-%d %H:%M:%S",
          "date": {
            "$toDate": "$lastCommGenTS"
          },
          "timezone": "+05:30"
        }
      },
      "lastupdatedIST": {
        "$dateToString": {
          "format": "%Y-%m-%d %H:%M:%S",
          "date": {
            "$toDate": "$lastUpdated"
          },
          "timezone": "+05:30"
        }
      },
      "lag_in_minutes": {
        "$divide": [
          {
            "$subtract": [
              "$lastUpdated",
              "$lastCommGenTS"
            ]
          },
          60000
        ]
      }
    }
  }
]

The error is:

Unexpected character ('{' (code 123)): was expecting double-quote to start field name at [Source: java.io.StringReader@6bab96b; line: 17, column: 26]

Hi @swapnilb
Please post “Diagnostic Info” from Admin > Troubleshooting.
What filter type is {{regNo}} ?

For reference: https://www.metabase.com/docs/latest/users-guide/13-sql-parameters.html