CORS ERROR - The 'Access-Control-Allow-Origin' header has a value 'http://localhost:3000/' that is not equal to the supplied origin. Node.js / Vue.js

I’m trying to make a side project to implement node.js with Vue.js. I’m stuck with this CORS error when I try to register a user on my register Vue Component. I tried many things I saw in stack overflow issues and node.js, CORS documentation,… but still I’m stuck with this error : The ‘Access-Control-Allow-Origin’ header has a value ‘http://localhost:3000/’ that is not equal to the supplied origin.

Here my index.js :

import mongoose from 'mongoose';
import user from './api/routes/user.js';
import express from 'express';
import dotenv from 'dotenv';
import cors from 'cors';
dotenv.config();

const app = express()
app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "http://localhost:8080/");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});
app.options('http://localhost:8080/', cors())

const corsOptions = {
  origin: 'http://localhost:8080/',
  optionsSuccessStatus: 200,
  methods: "GET, PUT, POST, DELETE"
}

mongoose.connect('mongodb://localhost/myDatabaseName', { 
    useNewUrlParser: true, 
    useUnifiedTopology: true 
} )
  .then(() => console.log('connected to mongoDb'))
  .catch((err) => console.error('could not connect to mongoDb..', err)); 

app.use(express.json())
app.use('/api/user', user)
app.use(cors(corsOptions));

const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Listening on port ${port}`))

First, I try only with CORS Lines (corsOption) and then without CORS lines, but it doesn’t work.

Here my Axios config file :

import axios, { AxiosRequestConfig } from 'axios';

const Axios = axios.create({
  // baseURL: process.env.VUE_APP_API_URL || '/api',
  baseURL: 'http://localhost:3000/api',
  withCredentials: true,
  headers: {
    'Content-Type': 'application/json',
  },
});

Axios.interceptors.request.use((config: AxiosRequestConfig) => {
  if (!config.method) {
    return config;
  }
  const method = config.method.toUpperCase();

  if (method !== 'OPTIONS') {
    config.headers = {
      ...config.headers,
      AUTHORIZATION: localStorage.getItem('JWT_ACCESS'),
    };
  }

  return config;
});

Here is my API call in my Vue.JS Component :

 private async submit() {
    try {
      const response = await registerApi.register(this.userBis);
      localStorage.setItem('JWT_ACCESS', response);
      localStorage.setItem('IS_SIGNED', 'true');
    } catch (err) {
      console.error(err);
    }
  }

Thanks in advance!

In the error you posted there is CORS error on port 3000, but in your headers you have port 8080.
Also I think the relevant methods should also be explicitly allowed.