The error library

Deploy, domains and hosting

• ERR_TOO_MANY_REDIRECTS after adding Cloudflare: Why a site behind Cloudflare loops with ERR_TOO_MANY_REDIRECTS and how SSL/TLS mode causes it.
• Cloudflare Error 1101: Rendering error (Worker exception): Why Cloudflare shows Error 1101 and how to find the Worker exception.
• CORS error after deploy: Access-Control-Allow-Origin missing: Why API calls fail with a CORS error only after deploying to a real domain, and how to fix the server response.
• Symptom: mixed content blocked on HTTPS site: Why images, scripts or API calls fail on an HTTPS site because they use http:// URLs, and the fix.
• SPA 404 on refresh: Vercel, Netlify, Cloudflare Pages: Why a React/Vite single-page app returns 404 when you refresh a route, and the rewrite rule each host needs.
• Symptom: CORS error calling Supabase Edge Function: Why browser calls to a Supabase Edge Function fail with CORS and how to add CORS headers.
• Vercel FUNCTION_INVOCATION_FAILED (500): Why Vercel functions fail with FUNCTION_INVOCATION_FAILED and how to debug them.
• Vercel FUNCTION_INVOCATION_TIMEOUT (504 Gateway Timeout): Why Vercel functions time out with FUNCTION_INVOCATION_TIMEOUT and what to check.

Build errors

• Symptom: env vars undefined after Cloudflare Pages build: Why environment variables are undefined after deploying to Cloudflare Pages, and how to set them for the build.
• Next.js: React client hook in a Server Component: Why Next.js errors when useState or useEffect is used in a Server Component, and the fix.
• Next.js DynamicServerError: Dynamic Server Usage: Why next build throws DynamicServerError when cookies() or headers() lose their async context, and the fix.
• Next.js hydration error: Text content does not match server-rendered HTML: Cause and fix for React hydration mismatch errors in Next.js apps.
• Next.js next/image un-configured host: Why next/image rejects a remote image URL and how to configure images.remotePatterns.
• Next.js Module not found (Can't resolve): Common causes of 'Module not found' in Next.js builds and how to fix them.
• Next.js env var undefined in the browser: missing NEXT_PUBLIC_: Why Next.js env vars are undefined in client code and how NEXT_PUBLIC_ works.
• Next.js prerender error during build: Why next build fails while prerendering a page and how to find the cause.
• Error: supabaseUrl is required. (Vite env var missing VITE_ prefix, blank screen in production): Why a Vite app shows a blank screen in production when env vars lack the VITE_ prefix, and how to fix it.

Auth and sign-in

• Symptom: auth breaks on custom domain: Supabase Auth / Clerk redirect and cookie mismatch: Why sign-in redirects to localhost or the session disappears after moving to a custom domain, and how to configure Supabase Auth and Clerk.
• Clerk: auth() was called but Clerk can't detect usage of clerkMiddleware(): Why Clerk can't detect clerkMiddleware() in Next.js and how to fix the middleware file.
• Firebase auth/unauthorized-domain: Why Firebase sign-in fails with auth/unauthorized-domain on a custom domain and how to authorize it.
• OAuth redirect_uri_mismatch (Google sign-in): Why Google sign-in fails with redirect_uri_mismatch after moving to a custom domain, and how to fix it.
• Supabase Auth: email_not_confirmed: Why Supabase sign-in fails with email_not_confirmed and how to fix confirmation emails.
• Supabase Auth: invalid_credentials: Why Supabase sign-in returns invalid_credentials and what to check.
• Supabase Auth: over_email_send_rate_limit: Why Supabase stops sending auth emails with over_email_send_rate_limit and how to fix it for production.

Stripe and payments

• Stripe resource_missing: The ID provided isn't valid: Why Stripe returns resource_missing for a price, customer or product ID, and how to fix it.
• Stripe: Webhook payload must be provided as a string or a Buffer (raw body): Why stripe-node rejects a parsed JSON webhook body and how to pass the raw body.
• Stripe webhook signature verification failed: fix: Cause and fix for Stripe's 'No signatures found matching the expected signature for payload' webhook error.

Database and data access

• Symptom: Firestore permission denied by Security Rules: Why Firestore requests are denied by Security Rules and how to write rules that allow your users.
• Prisma Client on the edge runtime / bundled for the browser: Why Prisma throws 'unable to run in this browser environment' in Next.js or edge functions, and how to fix it.
• Supabase RLS: empty results or 'new row violates row-level security policy': Why Supabase queries return [] or error 42501 with Row Level Security enabled, and how to add correct policies.