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Issue with count in $facet

I have issue with the following query… Unable to get count correctly… i wanted to have unique count of mhoId

db.getCollection('billing_info').aggregate(
[
    {
        "$match": {
            "billing.receiptinfo.receipt_date": {
                "$gte": "2020-04-01",
                "$lte": "2020-04-25"
            },
            "billing.receiptinfo.payment_mode": {
                "$nin": [
                    "",
                    []
                ]
            },
            "billing.receiptinfo.payment_submitted": {
                "$lt": 1
            },
            "billing.receiptinfo.mho_id": {
                "$nin": [
                    null,
                    ""
                ]
            }
        }
    },
    {
        "$unwind": "$billing.receiptinfo"
    },
    {
        "$facet": {
            "orderDetails": [
                {
                    "$project": {
                        "billId": "$billing.billinginfo.billingid",
                        "orderId": "$billing.billinginfo.order_did",
                        "mhoId": "$billing.receiptinfo.mho_id",
                        "mhoName": "$billing.receiptinfo.mho_name"
                    }
                },
                {
                    "$group": {
                        "_id": {
                            "mhoId": "$mhoId"
                        },
                        "info": {
                            "$push": "$$ROOT"
                        }
                    }
                }
            ],
            "countOrder": [
                {
                    "$group": {
                        "_id": "$mhoId",
                        "count": {
                            "$sum": 1
                        }
                    }
                }
            ]
        }
    }
])
    "countOrder": [
        {
            "$group": {
                "_id": "$mhoId",
                "count": {
                    "$sum": 1
                }
            }
        }
    ]

The field mhoId - does it represent the value from "billing.receiptinfo.mho_id", or is it a separate field?