How to fix email_exists: Email address already exists in Supabase

const { data, error } = await supabase.auth.signUp({
  email: '[email protected]',
  password: 'password123'
});

if (error?.message === 'email_exists') {
  // Email confirmation is disabled - direct error
  console.log('Email already registered - redirect to login');
  return;
}

if (data?.user) {
  // Email confirmation enabled - check identities array
  if (data.user.identities && data.user.identities.length === 0) {
    console.log('Email already exists - redirect to login');
    return;
  }

  // New user created successfully
  console.log('Signup successful - check email for verification');
}

// Server-side only - never expose service_role key to client
import { createClient } from '@supabase/supabase-js';

const supabaseAdmin = createClient(
  process.env.NEXT_PUBLIC_SUPABASE_URL!,
  process.env.SUPABASE_SERVICE_ROLE_KEY!,
  {
    auth: {
      autoRefreshToken: false,
      persistSession: false
    }
  }
);

const { data, error } = await supabaseAdmin.auth.admin.createUser({
  email: '[email protected]',
  password: 'password123',
  email_confirm: true
});

if (error?.message?.includes('email already exists')) {
  // Email is registered - handle accordingly
  console.log('User already has account with this email');
  return;
}

// User created successfully
console.log('New user created');

CREATE OR REPLACE FUNCTION public.check_email_exists(email_to_check TEXT)
RETURNS BOOLEAN
LANGUAGE plpgsql
SECURITY DEFINER
AS $$
BEGIN
  RETURN EXISTS (
    SELECT 1 FROM auth.users WHERE email = email_to_check
  );
END;
$$;

-- Grant execute permission to authenticated users
GRANT EXECUTE ON FUNCTION public.check_email_exists(TEXT) TO authenticated;

const { data: emailExists, error } = await supabase.rpc('check_email_exists', {
  email_to_check: '[email protected]'
});

if (emailExists) {
  console.log('Email already registered - show login option');
  return;
}

// Email is free - proceed with signup
const { data, error } = await supabase.auth.signUp({
  email: '[email protected]',
  password: 'password123'
});

async function handleSignup(email: string, password: string) {
  const { data, error } = await supabase.auth.signUp({
    email,
    password
  });

  // Handle explicit email_exists error
  if (error?.message === 'email_exists') {
    showMessage('This email is already registered. Please log in or reset your password.');
    redirectToLogin();
    return;
  }

  // Handle other errors
  if (error) {
    showError(error.message);
    return;
  }

  // Check for obfuscated response (email confirmation enabled)
  if (data?.user?.identities?.length === 0) {
    showMessage('An account with this email already exists. Please log in.');
    redirectToLogin();
    return;
  }

  // Successful signup
  showMessage('Account created! Check your email to verify.');
}