Row Level Security (RLS) Policy Blocks All Database Access

1. RLS enabled but no SELECT policy exists for authenticated users
2. Policy checks auth.uid() but user doesn't exist in referenced table
3. Policies use != 'anonymous' instead of checking specific roles
4. RLS conflicts between multiple overlapping policies
5. Missing USING or WITH CHECK clauses in policy definition

Create a basic policy allowing authenticated users:

CREATE POLICY 'Users can view own data'
ON public.users
FOR SELECT
USING (auth.uid() = id);

Verify policies in Supabase dashboard > Authentication > Policies. Test with Supabase Console Query Editor to debug specific queries.