Login as admin Create a new user leaving as many fields blank as possible Note its user name for later (substitute for the USERNAME in the CLI commands below) Go to Site administration ► Plugins ► Web services ► Mobile and tick Enable web services for mobile devices Create an external service in which core_user_get_users_by_field is added (You may also skip this and just use the built-in Moodle mobile web service ) Go to Site administration ► Plugins ► Web services ► Manage tokens Create a token for the admin user in that service Open a terminal window in which you'll observe your Apache error log Typically: {tail -f /var/log/apache2/error.log} Request the following: // Using HTTPie http -f WWWROOT/webservice/rest/server.php wstoken=TOKEN wsfunction=core_user_get_users_by_field field=username values[0]=USERNAME moodlewsrestformat=xml   // Using curl curl WWWROOT/webservice/rest/server.php -d wstoken=TOKEN -d wsfunction=core_user_get_users_by_field -d field=username -d values[0]=USERNAME -d moodlewsrestformat=xml Confirm that there aren't any notices/errors about missing indexes in the logs Confirm that the XML structure is not broken (does not contain notices either)