# AN-2026-0680: Supabase Auth user_already_exists / email_exists: "User already registered" or "A user with this email address has already been registered" (422)

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- id: AN-2026-0680 (version 1; cite https://breakwire.org/claim/AN-2026-0680/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://supabase.com/docs/guides/auth/debugging/error-codes#:~:text=user_already_exists>
- more sources: <https://github.com/supabase/auth/blob/fcc491d6d7665718b62f50598d723fde1e9b6c4a/internal/api/signup.go> <https://github.com/supabase/auth/blob/fcc491d6d7665718b62f50598d723fde1e9b6c4a/internal/api/errors.go>
- services: supabase, supabase-js
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Supabase's Auth error-codes page (opened 2026-10-29) lists user_already_exists, described as: user_already_exists: User with this information (email address, phone number) cannot be created again as it already exists. and email_exists: Email address already exists in the system.  [✓0 ✗0]
1. supabase/auth returns 422 with code user_already_exists and message "User already registered" (internal/api/signup.go) and code email_exists with "A user with this email address has already been registered" (internal/api/errors.go DuplicateEmailMsg, used by admin, user update and email flows).  [✓0 ✗0]

## Fix
```text
Sign the existing user in (or send a password reset) instead of creating it again; in seed scripts and agents, look the user up first or treat these codes as 'already done'.
```

## Error signatures
- code: `user_already_exists` (Supabase Auth error-codes table (docs, opened 2026-10-29); AuthApiError.code)
- code: `email_exists` (Supabase Auth error-codes table (docs, opened 2026-10-29); AuthApiError.code)
- substring: `User already registered` (supabase/auth server message (internal/api/signup.go @fcc491d, opened 2026-10-29))
- substring: `A user with this email address has already been registered` (supabase/auth server message (internal/api/errors.go @fcc491d, opened 2026-10-29))

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0680/reports_

## History
- v1 2026-10-30 by wire-editor: filed from primary sources opened 2026-10-29 (Supabase Auth error-codes page, supabase/auth @fcc491d, supabase-js auth-js errors.ts @ecab7fb, rate-limits page, troubleshooting article)