ejabberd connecting to admin "missing server"

Question

I'm trying to configure an ejabberd service that is working behind a public facing server. The latter sends https requests to the former via nginx reverse-proxy.

When accessing https://xmpp.example.cyou:5443/admin/ I place the credentials for user admin, but cannot log in. The log shows:

2021-07-27 12:12:12.548 [info] <0.396.0>@ejabberd_listener:accept:273 (<0.23212.0>) Accepted connection 44.44.55.55:57850 -> 192.168.7.5:5443
2021-07-27 12:12:12.592 [warning] <0.23212.0>@ejabberd_web_admin:process2:215 Access of <<"admin">> from <<"44.44.55.55">> failed with error: <<"missing-server">>

The ejabberd.yml configuration is:

hosts:
  - "example.cyou"
captcha_cmd: "/usr/local/bin/captcha.sh"
captcha_url: "http://@HOST@:5280/captcha"
captcha_limit: 5
loglevel: 4
certfiles:
  - "/usr/local/etc/ejabberd/certs/example.pem"
  - "/usr/local/etc/ejabberd/certs/example.cyou.key"
listen:
  -
    port: 5222
    ip: "192.168.7.5"
    module: ejabberd_c2s
    max_stanza_size: 262144
    shaper: c2s_shaper
    access: c2s
    tls: true
    starttls: true
    starttls_required: true
    protocol_options:
        - "no_sslv2"
        - "no_sslv3"
        - "no_tlsv1"
        - "no_tlsv1_1"
        - "no_tlsv1_3"
    ciphers: "ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256"
    dhfile:
      "/usr/local/etc/ejabberd/certs/c2s_dh2048.pem"
  -
    port: 5269
    ip: "192.168.7.5"
    module: ejabberd_s2s_in
    max_stanza_size: 524288
    dhfile:
      "/usr/local/etc/ejabberd/certs/s2s_dh2048.pem"
  -
    port: 5443
    ip: "192.168.7.5"
    module: ejabberd_http
    tls: true
    request_handlers:
      /admin: ejabberd_web_admin
      /api: mod_http_api
      /bosh: mod_bosh
      /captcha: ejabberd_captcha
      /upload: mod_http_upload
      /ws: ejabberd_http_ws
  -
    port: 5280
    ip: "192.168.7.5"
    module: ejabberd_http
    request_handlers:
      /admin: ejabberd_web_admin
  -
    port: 3478
    ip: "192.168.7.5"
    transport: udp
    module: ejabberd_stun
    use_turn: true
    turn_min_port: 49152
    turn_max_port: 65535
    turn_ipv4_address: 22.33.44.55
  -
    port: 1883
    ip: "192.168.7.5"
    module: mod_mqtt
    backlog: 1000
  -
    port: 5349
    transport: tcp
    module: ejabberd_stun
    use_turn: true
    tls: true
    turn_min_port: 49152
    turn_max_port: 65535
    ip: 192.168.7.5
    turn_ipv4_address: 22.33.44.55
s2s_use_starttls: optional
acl:
  local:
    user_regexp: ""
  loopback:
    ip:
      - 127.0.0.0/8
  admin:
      user:
          - "admin@example.cyou"
access_rules:
  local:
    allow: local
  c2s:
    deny: blocked
    allow: all
  announce:
    allow: admin
  configure:
    allow: admin
  muc_create:
    allow: local
  pubsub_createnode:
    allow: local
  trusted_network:
    allow: loopback
api_permissions:
  "console commands":
    from:
      - ejabberd_ctl
    who: all
    what: "*"
  "admin access":
    who:
      access:
        allow:
          - acl: loopback
          - acl: admin
      oauth:
        scope: "ejabberd:admin"
        access:
          allow:
            - acl: loopback
            - acl: admin
    what:
      - "*"
      - "!stop"
      - "!start"
  "public commands":
    who:
      ip: 127.0.0.1/8
    what:
      - status
      - connected_users_number
shaper:
  normal:
    rate: 3000
    burst_size: 20000
  fast: 100000
shaper_rules:
  max_user_sessions: 10
  max_user_offline_messages:
    5000: admin
    100: all
  c2s_shaper:
    none: admin
    normal: all
  s2s_shaper: fast
modules:
  mod_adhoc: {}
  mod_admin_extra: {}
  mod_announce:
    access: announce
  mod_avatar: {}
  mod_blocking: {}
  mod_bosh: {}
  mod_caps: {}
  mod_carboncopy: {}
  mod_client_state: {}
  mod_configure: {}
  mod_disco: {}
  mod_fail2ban: {}
  mod_http_api: {}
  mod_http_upload:
    docroot: "/var/spool/ejabberd/upload"
    put_url: "https://upload.@HOST@:5443"
    max_size: 10000000  #10MB
    file_mode: "0644"
    dir_mode: "0744"
    thumbnail: false
    access: local
  mod_last: {}
  mod_mam:
    assume_mam_usage: true
    default: always
  mod_mqtt: {}
  mod_muc:
    access:
      - allow
    access_admin:
      - allow: admin
    access_create: muc_create
    access_persistent: muc_create
    access_mam:
      - allow
    default_room_options:
      mam: true
  mod_muc_admin: {}
  mod_offline:
    access_max_user_messages: max_user_offline_messages
  mod_ping: {}
  mod_privacy: {}
  mod_private: {}
  mod_proxy65:
    access: local
    max_connections: 5
  mod_pubsub:
    access_createnode: pubsub_createnode
    plugins:
      - flat
      - pep
    force_node_config:
      storage:bookmarks:
        access_model: whitelist
  mod_push: {}
  mod_push_keepalive: {}
  mod_register:
    ip_access: all
    captcha_protected: true
  mod_roster:
    versioning: true
  mod_s2s_dialback: {}
  mod_shared_roster: {}
  mod_stream_mgmt:
    resend_on_timeout: if_offline
  mod_stun_disco: 
    credentials_lifetime: 12h
    services:
      -
        host: 192.168.7.5
        port: 3478
        type: stun
        transport: udp
        restricted: false
      -
        host: 192.168.7.5
        port: 3478
        type: turn
        transport: udp
        restricted: true
      -
        host: example.cyou
        port: 5349
        type: stuns
        transport: tcp
        restricted: false
      -
        host: example.cyou
        port: 5349
        type: turns
        transport: tcp
        restricted: true
  mod_vcard: {}
  mod_vcard_xupdate: {}
  mod_version:
    show_os: false

What is wrong? What is missing?

Answer 1

I place the credentials for user admin, but cannot log in.

Access of <<"admin">> from <<"44.44.55.55">> failed with error: <<"missing-server">>

You provided as account only "admin", and that is wrong.

As mentioned in https://docs.ejabberd.im/admin/guide/managing/#web-admin

You will be asked to enter the username (the full Jabber ID)
and password of an ejabberd user with administrator rights.

So, the credentials you must provide to login are: admin@example.cyou and the password.