To allow multiple user registration on Ejabberd server, we need to configure file ejabberd.yml in Ejabberd latest versions. Configure ejabberd.yml like: in access_rules: add

register:
    - allow
  register_from:
    - allow
  registration_timeout:
    - infinity

  mod_register:
    access_from:
      register_from
    access: 
      register

and in modules: add

 mod_register:
    access_from: register_from
    access: register

After adding these rules in ejabberd.yml file save it and run Ejabberd server and for checking purpose of these rules are really add or not so you can check it on Ejabberd server console, access_rules in raw file will looks like:

[{access, announce, [{allow, [{acl, admin}]}]},
 {access, c2s,
  [{deny, [{acl, blocked}]}, {allow, [all]}]},
 {access, c2s_shaper,
  [{none, [{acl, admin}]}, {normal, [all]}]},
 {access, configure, [{allow, [{acl, admin}]}]},
 {access, local, [{allow, [{acl, local}]}]},
 {access, max_user_offline_messages,
  [{5000, [{acl, admin}]}, {10000, [all]}]},
 {access, max_user_sessions, [{infinity, [all]}]},
 {access, mod_register,
  [{access_from, [{acl, register_from}]},
   {access, [{acl, register}]}]},
 {access, muc_create, [{allow, [{acl, local}]}]},
 {access, pubsub_createnode, [{allow, [{acl, local}]}]},
 {access, register, [{allow, [all]}]},
 {access, register_from, [{allow, [all]}]},
 {access, registration_timeout, [{infinity, [all]}]},
 {access, s2s_shaper, [{fast, [all]}]},
 {access, trusted_network, [{allow, [all]}]}].

and modules will look like:

mod_register:[{access_from, register_from},
 {access, register},
 {welcome_message,
  [{subject,
    <<87, 101, 108, 99, 111, 109, 101,
      33>>},
   {body,
    <<72, 105, 46, 10, 87, 101, 108, 99,
      111, 109, 101, 32, 116, 111, 32,
      116, 104, 105, 115, 32, 88, 77,
      80, 80, 32, 115, 101, 114, 118,
      101, 114, 46>>}]},
 {ip_access, trusted_network},
 {access, register}]

now your server is ready to register multiple users from different devices so quickly. Thank you.