How to Use Decimal128 in Loopback Via REST Api

I would like to utilise the MongoDB Decimal128 Data type in loopback. Note: I don't want to use the Number type.
My model:

{
  "name": "Mongoproduct",
  "options": {
    "validateUpsert": true,
    "strictObjectIDCoercion": true,
    "relations": {},
    "mongodb": {
      "collection": "products",
      "allowExtendedOperators": true
    }
  },
  "properties": {
    "id": {
      "type": "String",
      "required": true,
      "length": null,
      "precision": null,
      "scale": null
    },
    "sku": {
      "type": "String",
      "required": false,
      "length": 50,
      "precision": null,
      "scale": null,
    },
    "buyprice": {
      "type": "object",
      "mongodb": {
        "dataType": "Decimal128"
      }
    },
  }
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": {}
}

If I query the data through the REST explorer , a record will look something like this:

{
    "id": "5b41a6ac1afe940d900cba75",
    "sku": "shGHYB12-60-LOZ",
    "buyPrice": {
      "$numberDecimal": "20.4927"
    },
}

If I try and save the same data through a REST Put request , I get the following:

{
  "error": {
    "statusCode": 500,
    "name": "MongoError",
    "message": "The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.$numberDecimal' 
is not valid for storage.",
    "driver": true,
    "index": 0,
    "code": 52,
    "errmsg": "The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.$numberDecimal'
 is not valid for storage.",
    "stack": "MongoError: The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.
$numberDecimal' is not valid for storage.\n    at Function.MongoError.create (C:\\node
\\ztest\\ztest_data\\node_modules\\mongodb-core\\lib\\error.js:31:11)\n    at toError 
(C:\\node\\ztest\\ztest_data\\node_modules\\mongodb\\lib\\utils.js:139:22)\n    at 
C:\\node\\ztest\\ztest_data\\node_modules\\mongodb\\lib\\collection.js:1059:67\n    at
 C:\\node\\ztest\\ztest_data\\node_modules\\mongodb-core\\lib\\connection\\pool.js:469:18\n
    at process._tickCallback (internal/process/next_tick.js:61:11)"
  }
}

I have tried a number of things , different MongoDB types ( decimal , Decimal128 , NumberDecimal etc ) . I have tried putting allowExtendedOperators in the datasource config .
According to the loopback docs https://loopback.io/doc/en/lb3/MongoDB-connector.html#type-mappings:
Type conversion is mainly handled by Mongodb. See ‘node-mongodb-native’ for details
And According to the Native types https://docs.mongodb.com/manual/reference/bson-types/ I should be able to specify "decimal". ( I am using Mongodb 4.0 )
Any help is greatly appreciated.


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