Fixing Supabase RLS insert errors: three causes and the correct policy

Short summary

This post explains why the 'new row violates row-level security policy' error in Supabase is actually good news — RLS is working. It identifies three causes: no INSERT policy, mismatched user_id, or unauthenticated requests. The fix involves creating an INSERT policy with WITH CHECK and defaulting user_id server-side. Key gotchas include USING vs WITH CHECK semantics and testing through the app client rather than the SQL editor.

• •RLS error means security is working — don't disable it
• •Three causes: no INSERT policy, wrong user_id, or unauthenticated request
• •Fix: add INSERT policy with WITH CHECK and default user_id server-side

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