Create a course with groups enabled (visible, not forced), create a forum activity with visible groups Enrol a user as student in the course As admin, enable "Mobile services": Plugins ► Web Services ► Mobile Create a Token for the student user: Click on Site administration ► Plugins ► Web services ► Manage tokens Next, you can do a CURL REST call simulating a WS client with the student user. You need to replace the wstoken, cmid (with the forum course module id) and the URL of your moodle instance curl 'http://localhost/m/stable_master/webservice/rest/server.php?moodlewsrestformat=json' --data 'cmid=0&wsfunction=core_group_get_activity_groupmode&wstoken= ffbe3a3002f235bf9d01fd9369e10b66' Confirm that you receive a 2 (VISIBLEGROUPS) as response in the groupmode field Change the forum group mode to separate Run again the curl command, you should receive now a 1 as response Try to run the command using a cmid of an existing course module in a course you don't have access, you will receive an exception