Invalid redirect_uri in request Discord Oauth2

Question

I looked at other problems like mine, for example this one or this one. But the problems are because the URIs used aren't in the Redirect URIs in Discord OAuth2 config, and I checked them several times.

I have the following code:

import querySring from 'query-string'

// I'm using React Router for this
const code = searchParams.get('code')

if (!code) return

const data = {
      'client_id': 'my client id',
      'client_secret': 'my client secret',
      'grant_type': 'authorization_code',
      'code': code,
      'redirect_uri': querySring.stringifyUrl({ url: 'http://localhost:3000/login/callback' }),
}

const strData = querySring.stringify(data)   

const headers = {
      'Content-Type': 'application/x-www-form-urlencoded'
}

fetch('https://discord.com/api/oauth2/token', {
      method: 'POST',
      headers,
      body: strData,
})
  .then(res => res.json())
  .then(console.log)

And I get the following error:

error: "invalid_request",
error_description: "Invalid \"redirect_uri\" in request."

Of course, I made sure of having this redirect uri in the Discord Developer Portal:

I also tried using:

const data = {
    // ...
    'redirect_uri': 'http://localhost:3000/login/callback'
}

But nothing, I can't find what is wrong.