Flutter Web + Firebase: [firebase_auth/argument-error] - flutter

Question

I have a Flutter App that I'm simply building to web. I use pretty much the whole suite of Firebase tools. What happens is that whenever I try to call the any signIn method e.g. signInAnonymously or signInWithEmailAndPassword, I get an [firebase_auth/argument-error].
Regular firebase calls, like Firestore get() or update() are working fine.
This is my pubspec.yaml:
firebase_auth:
firebase_auth_web:
firebase_core:
firebase_core_web: ^1.7.3
firebase_storage:
firebase_analytics:
firebase_dynamic_links:
firebase_messaging:
cloud_firestore:
cloud_firestore_web:
cloud_functions:
I initialize Firebase like this in main.dart
if (Constants.BUILD_FOR_WEB) {
await Firebase.initializeApp(
options: const FirebaseOptions(
apiKey: '',
authDomain: '',
projectId: '',
storageBucket: '',
messagingSenderId: '',
appId: '',
),
);
} else {
await Firebase.initializeApp();
}
Note: I removed all firebase configurations from index.html because I read that it isn't needed anymore. Since firestore calls worked after removing, I figured it was true.
What I am doing is simply calling my anonymousSignUp() function:
import 'package:firebase_auth_web/firebase_auth_web.dart' as authWeb;
import 'package:firebase_auth/firebase_auth.dart' as auth;
Future<void> anonymousSignUp() async {
try {
if (Constants.BUILD_FOR_WEB) {
await _authWeb.signInAnonymously();
} else {
await _auth.signInAnonymously();
}
} catch (e) {
print(e);
}
}
I get an [firebase_auth/argument-error], nothing more.
No console output, nothing in the network tab either.
I don't know what to do. If anybody has a clue, I'm incredibly thankful for everything.