Error when trying to edit a field in a subdocument with mongoose. codeName: BadValue

Hello everyone,
I’m trying to edit subdocuments with mongoose, but I’m having problems.

I have a “Producer” model that references the “User” model like this:

user: {
    type: mongoose.Schema.Types.String,
    ref: 'User',
    required: true

This is the method I use to try to edit.

Producer.findByIdAndUpdate({ _id: },
		{"$set": {"user.$.name" : "John" }}, {"new": true}, function (err, doc) {
			(err ? res.status(400).send(err) : res.status(200).json(doc));

I’m doing the test using the postman, using the PUT method.

This is the return I get:

enter image description here

I appreciate if anyone can help me analyze this!

In the “Producer” document, the reference to “User” looks like this:

user: ObjectId(“6238d433980fba1bc09ae359”)