adding user in sys_user_grmember table from BR

Hafsa1
Mega Sage
I'm using simple BR on HR task table to insert user in groups. But it in not working. When I'm running this via admin, it is working, but when with other user then it is not adding user to group. Anything I'm missing?
 
var grp = current.groups.toString(); //Group to execute action against
    var grps = grp.split(',');
    var subject = current.opened_by; //Get User to execute action against
  for (var i = 0; i < grps.length; i++) {
        var grMbr = new GlideRecord('sys_user_grmember'); //Initiate Glide against Group membership table
        //Add Group membership  
        grMbr.initialize();
        grMbr.user = subject;
        grMbr.group = grps[i];
        grMbr.insert();
    }