A bunch of similar questions answered before but none of them seem to fix my problem. No problem in adding the first user. However, the username doesn't display the records and gives error on adding the second user.

```
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const userSchema = new Schema(
    {
        username: {
            type: String,
            unique: true,
            required: true,
            minlength: 3,
        },
        gender: String,
        age: Number
    },
    {
        timestamps: true
    }
);

const User = mongoose.model('user', userSchema);
module.exports = User;

```

[The error that I'm getting](https://i.stack.imgur.com/bpamq.png)

[The record on adding first user](https://i.stack.imgur.com/mdp1e.png)