Trouble with mongoDB Ref -> trying to ref array of diferent model - node.js

Question

so i'm trying ref a array of daysOff (Ferias model) as a fiel in a User model,
i'm new to MongoDB and mongoose, and i'm trying to build a API that manages a company workers days off.
I apologyse in advance for the "format" of this question but it's the very first time that I post a question in StackOverflow :)
Thanks u all!
const mongoose = require("mongoose");
const moment = require("moment");
const feriasSchema = mongoose.Schema(
{
user: {
type: mongoose.Types.ObjectId,
required: true,
ref: "User",
},
firstName: {
type: String,
ref: "User",
},
lastName: {
type: String,
ref: "User",
},
workerNumber: {
type: Number,
ref: "User",
},
sectionOfWork: {
type: String,
ref: "User",
},
totalFerias: {
type: Number,
required: true,
},
//this is the field i want to add in User model as an array of (dates format DD/MM/YYYY)
ferias: {
type: [String],
//default: [Date],
required: true,
},
tipoFerias: {
type: String,
required: true,
},
modo: {
type: String,
required: true,
},
},
{ timestamps: true }
);
module.exports = mongoose.model("Ferias", feriasSchema);
// USER MODEL
const userSchema = mongoose.Schema(
{
firstName: {
type: String,
required: true,
},
lastName: {
type: String,
required: true,
},
email: {
type: String,
required: [true, "Please enter a valid email address"],
unique: true,
},
password: {
type: String,
required: [true, "Please enter a password"],
},
workerNumber: {
type: Number,
required: true,
unique: true,
},
sectionOfWork: {
type: String,
required: true,
},
chefia: {
type: String,
required: true,
},
//this is the field i want to be an array (from Ferias model)
ferias: [{
type: mongoose.Schema.Types.ObjectId,
ref: "Ferias",
}],
role: {
type: String,
required: true,
},
},
{ timestamps: true }
);
module.exports = mongoose.model("User", userSchema);
what am i doing wrong?
i'm getting and empty array ...
in express I can send the questioned data separately but u want to send a json to some frontend with all the fields of a user, with the "ferias" array present.