Trying to split Mongoose models out into sud documents

I'm sure this is a syntax issue somewhere along the way. I've got a Mongoose model where part of it looks like this:

SMS_Data: {
        _id: false,
        SMS_User: [{
            Username: {
                type: String
            },
            Password: {
                type: String
            }
        }]
    }

This works fine, but I'm trying to split things out into subdocuments. So I've created a SMS_User.js model that looks like this:

const mongoose = require('mongoose');
const sms_user = mongoose.Schema({
    SMS_User: {
        Username: {
            type: String
        },
        Password: {
            type: String
        }
    }
})
module.exports = sms_user;

I require it into the main model using:
const sms_user = require('./SMS_User');

And tried changing the main model to now read like this:

SMS_Data: {
        _id: false,
        SMS_User: [sms_user]
    }

But this doesn't work. Instead of selecting the user I expected, based on the Username and Password. But when I use this from my login controller:

const user = await my_model.findOne({ 'SMS_Data.SMS_User.Username': userId, 'SMS_Data.SMS_User.Password': userPw });

it just selects the first record in the collection, instead of the correct one when I use the un-nested version of the model. Which suggest to me that the nesting of the sub model is wrong.

Like I say this could be glaringly obvious, but I'm just not seeing where I'm going wrong.

Thanks in advance.

the way you have broken down the schema is wrong since you have added an extra level of nesting (i.e 'SMS_Data.SMS_User.SMS_User.Username' etc).

You need to remove the SMS_User from sms_user schema

  const sms_user = mongoose.Schema({
    Username: {
      type: String
    },
    Password: {
      type: String
    }
  })
  const parentSchema = mongoose.Schema({
    //other fields
    SMS_Data: {
      _id: false,
      SMS_User: [sms_user]
    }
  })