You have set up your Supabase table. You have enabled Row Level Security (RLS). You even wrote an INSERT policy that explicitly allows authenticated users to create rows. Yet, when your frontend tries to save data, the database throws the dreaded error: 42501: new row violates row-level security policy for table "xyz" This is one of the most frustrating errors in PostgreSQL development because it feels like a lie. You permitted the insert, but the database says you didn't. The problem usually isn't your INSERT policy. The problem is that Supabase (via PostgREST) attempts to read the row immediately after writing it, and your policies don't allow that read operation. Here is the technical breakdown of why this happens and how to fix it properly. The Root Cause: The Hidden "Select" To understand the error, you must understand what happens under the hood of the Supabase JavaScript client. When you run a standard insert command in a modern React ...
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