AI & TechnologySupabase Database and Edge Function Errors: 12 Fixes (2026)

Short answer: Supabase errors outside sign-in come from three places: row level security and the API in front of the database, the connection and project itself, and Realtime and Edge Functions. Find your error below; each one links to a full fix page checked against the Supabase documentation.

Supabase database and Edge Function errors are easiest to fix once you know which layer threw them. The 12 errors below stop apps from reading, saving or calling functions, including apps generated by AI builders. Facts come from the vendors’ own documentation, as checked on the linked fix page; the advice on what to do and in which order is App369’s. For sign-in and email errors, see the Supabase Auth errors guide.

Query errors: row level security, PGRST116 and the schema cache

These four errors come back from the Supabase API when a query runs. Three of them involve row level security, which decides which rows each user can read or write.

“new row violates row-level security policy for table”

With row level security on, every operation needs its own policy, so a SELECT policy alone doesn’t allow inserts. Add an INSERT policy with a WITH CHECK clause, and set user_id from the signed-in session. Calling .select() after the insert also needs a SELECT policy: the PostgreSQL docs say “If a newly inserted or updated row does not satisfy the relation’s SELECT policies, an error will be thrown”. Full steps: new row violates row-level security.

Select returns an empty array, but the data is there

The Supabase RLS docs say “Once RLS is enabled, no data is accessible through the API when using a publishable key, until you create policies.” Add a select policy, make sure the query runs after the session loads, and check the rows carry this user’s ID. A 42501 error instead of an empty array means a missing grant. Full steps: Supabase select returns an empty array.

PGRST116: .single() got no row, or more than one

.single() expects exactly one row. Use .maybeSingle() when the row is optional, check that row level security lets this user read it, and filter on the primary key or add a unique constraint when duplicates match. Full steps: Supabase PGRST116.

“Could not find the table … in the schema cache” (PGRST205)

First check the table exists in the project your app’s Supabase URL points at; if it does, reload the schema cache from the SQL Editor. For a custom schema, the Supabase docs say “When multiple schemas are exposed, the first entry in the list is treated as the default, so PostgREST resolves unqualified object names only against that schema.” Full steps: Supabase schema cache error.

Connection, deploy and project errors

These four errors come from the connection, the deploy process or the state of the project, not from a single query.

“too many connections” or “remaining connection slots are reserved”

Check how many connections are in use in the dashboard first. For serverless code, the Supabase docs describe the transaction pooler: “Use it for serverless and edge functions, which open many short-lived connections.” Create the database client once and set its pool to 1 connection. Full steps: Supabase too many connections.

“TypeError: Failed to fetch” on a published app

In a Vite app, the Supabase URL has to be set where the published app is built, because Vite’s docs say “Variables prefixed with VITE_ will be exposed in client-side source code after Vite bundling.” A paused project, an Edge Function CORS error or a browser extension can cause it too. Full steps: Supabase Failed to fetch.

The project is paused and the app is down

Supabase pauses Free Plan projects with low activity over 7 days. Click Resume project in the dashboard, then check your main tables and flows. To stop it happening again, the Supabase docs say “Projects under a paid plan cannot be paused and are not subject to automatic pausing for inactivity.” Full steps: Supabase project paused.

supabase db push fails

Run supabase migration list to see which migrations exist only locally or only on the live database, and back up first. The Supabase migration docs warn that “Making schema changes directly on your remote database (via the SQL editor or Table Editor) bypasses the migration history and will cause db push to fail with sync errors.” Full steps: Supabase db push failed.

Realtime and Edge Function errors

These four errors appear in code that runs outside a plain query: Realtime subscriptions and Edge Functions. Each fix page lists the causes in the order to check them.

Realtime is subscribed, but no changes arrive

The Supabase Realtime troubleshooting guide says “Realtime doesn’t watch every table by default. Each one has to be added to a publication called supabase_realtime.” Realtime also applies row level security as the subscribing user, so check the policy lets that user select the row. Full steps: Supabase Realtime not receiving changes.

Edge Function call blocked by CORS policy

The browser sends an OPTIONS preflight first, and the function has to answer it with CORS headers. Add the headers to every response, including errors, or the browser reports CORS instead of the real error. With JWT verification on, a missing or wrong Authorization header gets a 401 before your code runs. Full steps: Supabase Edge Function CORS error.

Edge Function times out with a 504 or 546

According to the Supabase Edge Functions limits, “If an Edge Function doesn’t send a response before the timeout, 504 Gateway Timeout will be returned”. The timeout is 150 seconds. A 546 is a resource limit, such as 2 seconds of CPU time or 256MB of memory, and the logs name which one. Full steps: Supabase Edge Function timeout.

“Edge Function returned a non-2xx status code”

The function ran and sent back an error; the Supabase docs describe it as “FunctionsHttpError: Your function executed but returned an error (4xx/5xx status)”. Read the response body in error.context and the function’s logs in the dashboard. Full steps: Edge Function non-2xx status code.

Which to check first

The fastest route is the exact error text, or the empty result, and the request that produced it in the browser’s Network tab. App369’s full order for a Supabase app that just broke:

1. Check the project is running and the app points at the right project URL.
2. Run the same query as the same user, signed in, and see whether row level security hides the rows.
3. For an Edge Function, open its logs in the dashboard before changing code.
4. For connection errors, check how many connections are in use and whether serverless code uses the pooler.
5. Check what changed since it last worked: migrations, policies, environment variables.

The Supabase errors and fixes page lists every Supabase fix. Before launch, the Supabase security review covers the settings to check.

Need a hand?

App369 fixes single Supabase database and Edge Function bugs at a fixed price. If one bug is the whole problem, the App Fix Ticket covers it in two fixed-price steps: a $450 diagnosis that finds the root cause and gives you a fixed quote for the fix, then the fix itself. If the app was built with an AI builder and more is going on, the AI-Built App Rescue starts with a Launch Check of the whole app. Or describe the problem and get a written quote.