Help with OAuth2

Hey! So I’m new to Oauth2 and need some help getting set up… I’m trying to create a rank-locked portal on my website which has admin stats. The reason I want to use Roblox as an authentication/login method is because this admin dashboard needs to be locked for certain ranks in my group.

I’ve even consulted ChatGPT to help me with this, as i get the same errors each time I try:
{"errors":[{"code":0,"message":"NotFound"}]}

As far as I’m aware, you don’t need your app published/approved whilst its in testing, at least up to 100 members so this shouldn’t be an issue? Anyways, I’m using passport as the authentication handler for my site and here’s a snippet from my code, is anything wrong here? Am I just being stupid?
(js)

passport.use(new OAuth2Strategy({
  authorizationURL: 'https://auth.roblox.com/oauth/authorize',
  tokenURL: 'https://auth.roblox.com/oauth/token',
  clientID: 'im not this stupid to show it here!',   
  clientSecret: 'and this too',
  callbackURL: 'https://mydomain.xyz/auth/callback', 
},
(accessToken, refreshToken, profile, done) => {
  return done(null, { accessToken });
}));

My domain is correct, set up and all managed already so I’m not using localhost for this project.
And yes, the links for callback, redirect, and policy all match exactly, so it’s not to do with that.
Any help would be greatly appreciated!