Linking Firebase with Unity doesn't work?

I don't understand what instructions the tutorial gave you. Please give more information as to what tutorial you're following and what you're trying to accomplish.

By 'linking firebase to Unity', do you mean that you want to access your Firebase database from Unity? If so, all you need is the 'google-services' json file provided from the database, and you'll need to install the Firebase Unity packages from their website.

Then, in your C# script, you should have the Firebase namespace (as well as external namespaces depending on what other packages you have, such as Firebase.Database). From the json file, get the text, and then create a new Firebase app from that text using:

 AppOptions settings = AppOptions.LoadFromJsonConfig(jsonConfig);
 FirebaseApp app = FirebaseApp.Create(settings);
 

From there, you can get your realtime database reference through:

 FirebaseDatabase database = FirebaseDatabase.GetInstance(app);

And so on.. Hope that helped @Radical_boy