Error reference.
Each user-recoverable error in Citadel has a short identifier you can quote to support. Where it adds something, a dedicated help page links from the catalog. Scroll for the full list.
Error reference
E-client_is_public
Public clients have no secret to rotate.
E-display_name_too_long
Display name must be 80 characters or fewer.
E-identity_already_linked
That provider account is already linked to a different Citadel account.
E-identity_email_mismatch
The provider returned a different email than the one on your Citadel account.
E-identity_link_failed
The link couldn't be completed.
E-identity_provider_unavailable
That provider isn't available right now.
E-invalid_email
That doesn't look like a valid email address.
E-invalid_format
Username can only contain letters, digits, and hyphens.
E-invalid_redirect_uri
A redirect URI is invalid.
E-is_public_immutable
Public/confidential cannot be changed after creation.
E-name_required
Name is required.
E-rate_limited
Too many sign-in attempts.
E-redirect_uris_required
At least one redirect URI is required.
E-reserved
That username is reserved by Citadel.
E-slug_taken
Someone took that name a moment ago.
E-too_long
Username must be at most 39 characters.
E-too_short
Username must be at least 3 characters.
E-unknown_provider
That provider isn't enabled.