Aggregation Error: $lookup with 'pipeline' may not specify 'localField' or 'foreignField'

I'm trying to translate this aggregation to one within lookup but not successful

db.users.aggregate([
    { $match: { "medicalPractice.consultation.slots": { $exists: true } } },
    {
        "$addFields": {
            "slots": {
                $reduce: {
                    input: '$medicalPractice.consultation',
                    initialValue: [],
                    in: {
                        $concatArrays: [
                            "$$value",
                            {
                                $map: {
                                    input: '$$this.slots',
                                    as: "slot",
                                    in: {
                                        slot: "$$slot"
                                    }
                                }
                            }]
                    }
                }
            }
        }
    },
    {
        "$addFields": {
            slotsLength: {
                $size: "$slots"
            }
        }
    }
    
])

Here is what I'm trying:

db.profiles.aggregate([
    {
        $lookup: {
            from: 'users',
            localField: 'user',
            foreignField: '_id',
            as: 'user',
            let: { consultation: "$medicalPractice.consultation" },
            pipeline: [
                {
                    "$addFields": {
                        "slots": {
                            $reduce: {
                                input: '$$consultation',
                                initialValue: [],
                                in: {
                                    $concatArrays: [
                                        "$$$value",
                                        {
                                            $map: {
                                                input: '$$$this.slots',
                                                as: "slot",
                                                in: {
                                                    slot: "$$$slot"
                                                }
                                            }
                                        }]
                                }
                            }
                        }
                    }
                },
                {
                    "$addFields": {
                        slotsLength: {
                            $size: "$$$slots"
                        }
                    }
                }
            ]
        },
    },
    {
        $limit: 10
    }
])

But for some reason still get this error "$lookup with 'pipeline' may not specify 'localField' or 'foreignField'"