Unhandled rejection MongoError: The dollar ($) prefixed field '$inc' in '$inc' is not valid for storage

You should include values as JSON in Mongo Query. Might be due to this you are facing an issue. Can you please try by updating your query as:

APILog.update({
  "apiId": 1
},
{
  "$inc": {
    "dataCount": 10
  }
})

I ran into same exception and was able to solve this way. Following is the syntax of executing a general command in mongodb, updated with your example data:

db.runCommand(
    update: "<replace-with-collection-name>",
    updates: [
        {
            q:{"apiId": 1}, u: {"$inc": {"dataCount": 10}}
        }
    ]
)

Escape the $ character as per rules of node.js, if needed.

Since I came across this... I've found at least for me that it works to use brackets if you're doing an aggregation inside your update. Like so:

db.example.updateMany(
    {FirstRecord:{$in:recordids}},
    [{$set:{
        RecordCode:{
            $first:{
                $map:{
                    ...
                }
            }
        }
     }}]
 )

In my case I'm trying to update a field which is a code we will use later to match to other documents, and have a list of ObjectIds for the target records and a dictionary from ID to code. Anyway I found I received a similar error until I added the brackets around [{$set:{}}]