Issue with $push operator

I am currently working on a web scraping project. The goal is to retrieve the price of the different types of fuel available in the gaz stations (900+) each day . If the price changes, the script will be able to append the new price to my Mongodb database.

The data collected looks like this:

Price_post_api = {

    "station_id": 31200009,
    "price_detail": [
      {
        "fuel_id": 1,
        "fuel_name": "Gazole",
        "fuel_cost": 1.959,
        "update_date": {
          "$date": "2022-05-30T10:05:22Z"
        }
      },
      {
        "fuel_id": 2,
        "fuel_name": "SP95",
        "fuel_cost": 2.049,
        "update_date": {
          "$date": "2022-05-30T10:05:23Z"
        }
      },
      {
        "fuel_id": 5,
        "fuel_name": "E10",
        "fuel_cost": 2.009,
        "update_date": {
          "$date": "2022-05-30T10:05:23Z"
        }
      }
    ]
  },

I’m having a hard time to figure out how to $push properly the data in Mongodb based on the "fuel_cost" field. Here an example of the expected output in the db.

Mongodb_price_data ={
    "station_id": 31200009,
    "price_detail": [
      {
        "fuel_id": 1,
        "fuel_name": "Gazole",
        "fuel_cost": 1.959,
        "update_date": {
          "$date": "2022-05-30T10:05:22Z"
        }
      },
      {
        "fuel_id": 1,
        "fuel_name": "Gazole",
        "fuel_cost": 35.87,
        "update_date": {
          "$date": "2022-05-31T10:09:22Z"
        }
      },
      {
        "fuel_id": 2,
        "fuel_name": "SP95",
        "fuel_cost": 2.049,
        "update_date": {
          "$date": "2022-05-30T10:05:23Z"
        }
      },
      {
        "fuel_id": 2,
        "fuel_name": "Gazole",
        "fuel_cost": 1.59,
        "update_date": {
          "$date": "2022-07-14T00:10:19Z"
        }
      },
      {
        "fuel_id": 5,
        "fuel_name": "E10",
        "fuel_cost": 2.009,
        "update_date": {
          "$date": "2022-05-30T10:05:23Z"
        }
      }
    ]
}

So far, I have the following function:

def update_new_price(station_id, fuel_id, fuel_name, cost):
    query = {'station_id': station_id, 'price_detail.fuel_id': fuel_id,
             'price_detail.fuel_name': fuel_name, 'price_detail.fuel_cost': cost}

    result = db[CL_PRICE].find(query)

    if not list(result):
        db[CL_PRICE].update_one(
            {'station_id': station_id, 'price_detail.fuel_id': fuel_id,
                'price_detail.fuel_name': fuel_name},
            {'$push': {'price_detail': {'$each': [
                {'fuel_id': fuel_id, 'fuel_name': fuel_name, 'fuel_cost': cost}]}}},upsert=True)
        print('new value added: ', {'station_id': station_id, 'fuel_id': fuel_id, 'fuel_name': fuel_name, 'fuel_cost': cost})
    else:
        print('Already exists: ', {'station_id': station_id, 'fuel_id': fuel_id, 'fuel_name': fuel_name, 'fuel_cost': cost})

The function works great until I get an error message

pymongo.errors.WriteError: The field 'price_detail' must be an array but is of type object in document {no id}, full error: {'index': 0, 'code': 2, 'errmsg': "The field 'price_detail' must be an array but is of type object in document {no id}"}

Any idea why and how can I fix it?