Admin page: Error deleting user 400

[dreamflasher]

Hi,
when trying to delete a user (or deactivate) I receive the error "Error deleting user 400 - [Catch] SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data".

I'd appreciate your help debugging this.

[stefan0xC]

Which version? Do you have customized admin templates?

[BlackDex]

Looks like a field has invalid json, could be a very very old user or something broke the database. But with a bit more details it might help.

[dreamflasher]

Support string:

Your environment (Generated via diagnostics page)

• Vaultwarden version: v1.36.0
• Web-vault version: v2026.4.1
• OS/Arch: linux/x86_64
• Running within a container: true (Base: Debian)
• Database type: SQLite
• Database version: 3.51.3
• Uses config.json: true
• Uses a reverse proxy: true
• IP Header check: true (X-Real-IP)
• Internet access: true
• Internet access via a proxy: false
• DNS Check: true
• Browser/Server Time Check: true
• Server/NTP Time Check: true
• Domain Configuration Check: true
• HTTPS Check: true
• Websocket Check: false
• HTTP Response Checks: true

Config & Details (Generated via diagnostics page)

Show Config & Details

Environment settings which are overridden: ADMIN_TOKEN

Config:

{
  "_duo_akey": null,
  "_enable_duo": false,
  "_enable_email_2fa": false,
  "_enable_smtp": true,
  "_enable_yubico": true,
  "_icon_service_csp": "",
  "_icon_service_url": "",
  "_ip_header_enabled": true,
  "_max_note_size": 10000,
  "_smtp_img_src": "***:",
  "admin_ratelimit_max_burst": 3,
  "admin_ratelimit_seconds": 300,
  "admin_session_lifetime": 20,
  "admin_token": "***",
  "allowed_connect_src": "",
  "allowed_iframe_ancestors": "",
  "attachments_folder": "data/attachments",
  "auth_request_purge_schedule": "30 * * * * *",
  "authenticator_disable_time_drift": false,
  "data_folder": "data",
  "database_conn_init": "",
  "database_idle_timeout": 600,
  "database_max_conns": 10,
  "database_min_conns": 2,
  "database_timeout": 30,
  "database_url": "***************",
  "db_connection_retries": 15,
  "disable_2fa_remember": false,
  "disable_admin_token": false,
  "disable_icon_download": false,
  "dns_prefer_ipv6": false,
  "domain": "*****://**********************",
  "domain_origin": "*****://**********************",
  "domain_path": "",
  "domain_set": true,
  "duo_context_purge_schedule": "30 * * * * *",
  "duo_host": null,
  "duo_ikey": null,
  "duo_skey": null,
  "duo_use_iframe": false,
  "email_2fa_auto_fallback": false,
  "email_2fa_enforce_on_verified_invite": false,
  "email_attempts_limit": 3,
  "email_change_allowed": true,
  "email_expiration_time": 600,
  "email_token_size": 6,
  "emergency_access_allowed": true,
  "emergency_notification_reminder_schedule": "0 3 * * * *",
  "emergency_request_timeout_schedule": "0 7 * * * *",
  "enable_db_wal": true,
  "enable_websocket": true,
  "enforce_single_org_with_reset_pw_policy": false,
  "event_cleanup_schedule": "0 10 0 * * *",
  "events_days_retain": null,
  "experimental_client_feature_flags": "",
  "extended_logging": true,
  "helo_name": null,
  "hibp_api_key": null,
  "http_request_block_non_global_ips": true,
  "http_request_block_regex": null,
  "icon_blacklist_non_global_ips": true,
  "icon_blacklist_regex": null,
  "icon_cache_folder": "data/icon_cache",
  "icon_cache_negttl": 259200,
  "icon_cache_ttl": 2592000,
  "icon_download_timeout": 10,
  "icon_redirect_code": 302,
  "icon_service": "internal",
  "incomplete_2fa_schedule": "30 * * * * *",
  "incomplete_2fa_time_limit": 3,
  "increase_note_size_limit": false,
  "invitation_expiration_hours": 120,
  "invitation_org_name": "Bitwarden_RS",
  "invitations_allowed": false,
  "ip_header": "X-Real-IP",
  "job_poll_interval_ms": 30000,
  "log_file": null,
  "log_level": "info",
  "log_timestamp_format": "%Y-%m-%d %H:%M:%S.%3f",
  "login_ratelimit_max_burst": 10,
  "login_ratelimit_seconds": 60,
  "org_attachment_limit": null,
  "org_creation_users": "",
  "org_events_enabled": false,
  "org_groups_enabled": false,
  "password_hints_allowed": true,
  "password_iterations": 100000,
  "purge_incomplete_sso_auth": "0 20 0 * * *",
  "push_enabled": false,
  "push_identity_uri": "https://identity.bitwarden.com",
  "push_installation_id": "***",
  "push_installation_key": "***",
  "push_relay_uri": "https://push.bitwarden.com",
  "reload_templates": false,
  "require_device_email": false,
  "rsa_key_filename": "data/rsa_key",
  "send_purge_schedule": "0 5 * * * *",
  "sendmail_command": null,
  "sends_allowed": true,
  "sends_folder": "data/sends",
  "show_password_hint": true,
  "signups_allowed": true,
  "signups_domains_whitelist": "",
  "signups_verify": false,
  "signups_verify_resend_limit": 6,
  "signups_verify_resend_time": 3600,
  "smtp_accept_invalid_certs": false,
  "smtp_accept_invalid_hostnames": false,
  "smtp_auth_mechanism": null,
  "smtp_debug": false,
  "smtp_embed_images": true,
  "smtp_explicit_tls": null,
  "smtp_from": "********************",
  "smtp_from_name": "***********",
  "smtp_host": "***************",
  "smtp_password": "***",
  "smtp_port": 587,
  "smtp_security": "starttls",
  "smtp_ssl": null,
  "smtp_timeout": 15,
  "smtp_username": "*********",
  "sso_allow_unknown_email_verification": false,
  "sso_audience_trusted": null,
  "sso_auth_only_not_session": false,
  "sso_authority": "",
  "sso_authorize_extra_params": "",
  "sso_callback_path": "*****://***************************************************",
  "sso_client_cache_expiration": 0,
  "sso_client_id": "",
  "sso_client_secret": "***",
  "sso_debug_tokens": false,
  "sso_enabled": false,
  "sso_master_password_policy": null,
  "sso_only": false,
  "sso_pkce": true,
  "sso_scopes": "email profile",
  "sso_signups_match_email": true,
  "templates_folder": "data/templates",
  "tmp_folder": "data/tmp",
  "trash_auto_delete_days": null,
  "trash_purge_schedule": "0 5 0 * * *",
  "use_sendmail": false,
  "use_syslog": false,
  "user_attachment_limit": null,
  "user_send_limit": null,
  "web_vault_enabled": true,
  "web_vault_folder": "web-vault/",
  "yubico_client_id": null,
  "yubico_secret_key": null,
  "yubico_server": null
}

[dreamflasher]

No error in the web console, I have -e LOG_LEVEL=debug -e EXTENDED_LOGGING=true -e LOG_FILE=/data/vaultwarden.log it also shows debug level messages, but no entry at the time of the error, I tried multiple times there is nothing in there related to the error.

[dreamflasher]

I made a full database export and import and that fixed the issue. Thank you for your help!

[yudin-s]

The popup mostly tells you that the admin page tried to parse JSON and got a non-JSON response back. The next useful detail is the response body for that delete/deactivate request: it may be a proxy HTML page, a login/redirect response, a Vaultwarden error, or a frontend/backend mismatch.

I would debug it in this order:

1. Open browser DevTools -> Network.
2. Try the delete/deactivate action again.
3. Click the failing request and check Status, Content-Type, and the first lines of the Response tab.
4. At the same time, watch the Vaultwarden container log.

If the response starts with HTML from your reverse proxy, test the same admin action by accessing Vaultwarden directly, bypassing the proxy. If it is Vaultwarden's own error text, paste the container log around that request.

The existing question about version/customized admin templates is important too. If you have mounted custom admin templates or copied old web assets, remove them and test with the admin page shipped by the same Vaultwarden image version. A newer backend plus stale admin frontend can easily produce a request/response shape the UI cannot parse.

Once you have the failing request's status, content type, response body, Vaultwarden version, and matching container log line, the cause should be much less guessy.

[dreamflasher]

Thank you @yudin-s for your help. I've responded in the thread above; there I posted the support string, and unfortunately even with debug level logging, it does not show any errors or anything related to the delete action.
The response tab shows the following for the failing request: Status 400, content-type text/html; charset=iso-8859-1,
And the reponse:

<title>400 Bad Request</title>
</head><body>
<h1>Bad Request</h1>
<p>Your browser sent a request that this server could not understand.<br />
</p>