Steam SignIn 401 unable to validate token

Hello, I'd like for my users to use steam to sign in to the the game, and after use friends list, etc... unfortunately I'm having an issue. When trying to log in with steam using

await AuthenticationService.Instance.SignInWithSteamAsync(m_SessionTicket);

This returns the following error :
[Authentication]: Request failed: 401, {"title":"PERMISSION_DENIED","detail":"unable to validate token","details":[ ],"status":401}

I have followed the steps and have added the identity provider with app id being 480 and the key I found https://steamcommunity.com/dev/apikey but it isn't working. I do think the error is related to the app id and key I have inputed but I cannot find a solution. Keep in mind I do not have a steamworks app as this is a project and I don't want to pay 100$ (that's why I put 480 in appid).
Please If you have any insight related to this, I'd really appreciate it.

Hi there,
You must have a valid AppID and account to be able to link with Steam.
The error you are getting seems to relate to you trying with an AppID that isn't yours?

Please refer to the following docs for more information:
https://docs.unity.com/authentication/en/manual/set-up-steam-signin

Let me know if it fails once you have your own AppID so I can continue helping you out.

I'm developing a game, and to be able to create an app, I need to pay 100$ to steam.
480 is supposed to be the developer code, but I don't want to pay if I don't need to.