Normal user is not able to assign role to himself and others

Hi Team

When I am creating any group as a normal registered user, I am calling an API '#set($addRole = $core_v2_roleUsers.AddUserToRole("%{ RoleName = '<role name>', UserId = <userid> }"))'  to add a role to particular normal user, but I am not able to assign that role. 

When I am calling the same API as an 'Administrator' while creating the group, it runs successfully and I am able to assign the role to myself and the others.

So could you please help me know whether a normal registered user has appropriate rights to assign any role to himself and the others or not.