I'm building a Next.js app with Firebase and email/password sign-up fails with auth/network-request-failed on both localhost and Vercel.

What I've tried:

✅ Enabled Identity Toolkit API in Google Cloud

✅ Added Vercel domain to Firebase authorized domains

✅ Enabled Email/Password provider in Firebase

✅ API key is unrestricted

✅ Restarted computer, tried incognito

✅ .env.local has correct Firebase credentials

Error:

FirebaseError: Firebase: Error (auth/network-request-failed)

Google Sign-In also fails with same error.

Environment: Next.js 16.1.6, Firebase SDK latest