Your RLS policies look fine – yet the Supabase client throws:

permission denied for table projects
ERROR: 42501

Or PostgREST shows 42501 / “permission denied”. This is not the same as new row violates row-level security policy. Here is how to tell them apart and fix the grants.

Your query looks correct – yet the Supabase JS client throws:

JSON object requested, multiple (or no) rows returned
code: PGRST116

This almost always comes from .single() (or .maybeSingle() misuse) when PostgREST did not get exactly one row. Here is how to fix it cleanly.

The Problem: .single() Means Exactly One Row

.single() tells PostgREST: return one JSON object. If the result set is empty or has more than one row, you get PGRST116 instead of data.

Common causes:

Your upload code looks correct, the user is signed in – yet Supabase Storage responds with:

StorageApiError: new row violates row-level security policy
statusCode: 403

You often already have an INSERT policy – and the upload still fails. Here is the fix most people miss.

Your login form looks fine, email and password seem correct – yet Supabase Auth responds with:

AuthApiError: Invalid login credentials

Or in the Network tab: 400 with error_description: "Invalid login credentials". Here are the most common causes and the fixes that reliably worked for me.

The Problem: What "Invalid login credentials" Really Means

For security reasons Supabase does not tell you whether the email or the password is wrong. That single message covers several cases:

You wrote an RLS policy that checks another table – and suddenly Supabase throws:

ERROR: infinite recursion detected in policy for relation "profiles"

In this article I'll show you why that recursion happens and how to fix it with a clean policy design (or a SECURITY DEFINER helper).

Your Edge Function works locally – but from the browser or via fetch you only get:

{"code":401,"message":"Invalid JWT"}

Or: Missing authorization header. This guide walks through fixing the 401 step by step – including when you should intentionally disable JWT verification.

The Problem: Why Edge Functions Return 401

Supabase Edge Functions can run a JWT check before your code. If that check fails, your function never runs – you only see a platform 401.

Typical triggers:

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