MongoDB: No write concern mode named 'majority a' found in replica set configuration - mongodb

Question

I am working through a traversy media tutorial and I've come across an error (in the title) that I'm not familiar with. I've been trying to learn about this but I'm still stumped as to why its appearing and where its coming from. Furthermore, I havent found any direct matches for this issue.
Here is the code in question, the catch at the bottom is returning the error.message.
edit: its also worth noting that I am able to successfuly add users to my database. So, it runs through the try block but also the catch ... so thats a big confusing. The only response I am getting on postman is the server error 500 message from the catch block.
const express = require('express');
const router = express.Router();
const gravatar = require('gravatar');
const bcrypt = require('bcryptjs');
const { check, validationResult } = require('express-validator');
const User = require('../../models/User');
// #route GET api/users
// #desc Test route
// #access Public
router.post(
'/',
[
check('name', 'Name is required').not().isEmpty(),
check('email', 'Please include a valid email').isEmail(),
check(
'password',
'Please enter a password with 6 or more characters'
).isLength({ min: 6 }),
],
async (req, res) => {
const errors = validationResult(req);
if (!errors.isEmpty()) {
return res.status(400).json({ errors: errors.array() });
}
const { name, email, password } = req.body;
try {
let user = await User.findOne({ email });
// see if user exists
if (user) {
return res.status(400).json({
errors: [{ msg: 'User already exists' }],
});
}
// get users gravatar
const avatar = gravatar.url(email, {
s: '200',
r: 'pg',
d: 'mm',
});
user = new User({
name,
email,
avatar,
password,
});
// encrypt password
const salt = await bcrypt.genSalt(10);
user.password = await bcrypt.hash(password, salt);
await user.save();
// return jsonwebtoken
return res.send('User registered');
} catch (error) {
console.log(error.message);
res.status(500).send('Server error');
}
}
);
module.exports = router;
The User schema
const mongoose = require('mongoose');
const UserSchema = new mongoose.Schema({
name: {
type: String,
required: true,
unique: true,
},
email: {
type: String,
required: true,
unique: true,
},
password: {
type: String,
required: true,
},
avatar: {
type: String,
},
date: {
type: Date,
default: Date.now,
},
});
const User = mongoose.model('user', UserSchema);
module.exports = User;
connection configuration:
const mongoose = require('mongoose');
const config = require('config');
const db = config.get('mongoURI');
const connectDB = async () => {
try {
await mongoose.connect(db, {
useUnifiedTopology: true,
useNewUrlParser: true,
useCreateIndex: true,
});
console.log('Connected to MongoDB');
} catch (err) {
console.error(err.message);
process.exit(1);
}
};
module.exports = connectDB;