//As per Quention's advice, I needed to add http:// in front of localhost:3001. The code became:
const url = new URL("http://localhost:3001")
//Afterwards, I needed to enable cors on my server in order to fix another error.
//Because I was using express, I just ran npm install cors and then added the following 2 lines to my server:
//use it in top your Express app
const cors = require("cors")
app.use(cors())