Error: Cannot find module 'express'

I had a notebook that had been working months ago, but suddenly, it stoped working. When I browse endpoint, I get this error,

{
“error”: “initialization_error”,
“message”: “There was an error initalizing your endpoint.”
}

I haven´t done any change, so maybe something changed in runkit that I never knew.

this is the begining of my code:

const express = require(‘express’);
const app = express();
app.use(express.json());

app.get(‘/’, (req, res) => res.send(‘Hello World! n’));

app.listen(3000, () => console.log(‘Example app listening on port 3000!’));

// POST method route
app.post(‘/’, function (req, res) {