Registration is currently disabled
New account creation is turned off. Email POST /api/auth/register returns 403 AUTH_REGISTRATION_DISABLED; OAuth signup uses the same user-facing line (oauthRegistrationDisabled).
Why this happens
isRegistrationOpen() is false — Registration enabled setting off (or equivalent). Existing members can still sign in if Login enabled is on. Not a captcha or validation error.
Diagnose and fix
1. Admin: enable Registration enabled under site/auth settings; save.
2. Confirm the register page loads open (not a closed banner).
3. Social: new OAuth users also require registration open; linking to an existing email account may still work when configured.
4. Distinct from Registration could not be completed (open but create failed).