Cannot set relationship between users and roles through rest api

Hi,

I am trying to use the set_relationship function of suite rest api, to add a relation to the users. But I am unable to get it successsfully inserted into database.
I am not getting any error in the response also.

I am using .net C#.
The code to set relationship that I am using is :
List relatedIds = new List
{ roleid};

            req.module_name = "Users";
            req.module_id = userid;
            req.link_field_name = "ACLroles";
            req.name_value_list = new List<string>()
            {

            };
            req.related_ids = relatedIds;

Am I doing anything wrong here? I checked for vardefs.php file too to get the relationshipname for users and roles, but did not find it. so used the linkfield name as ACLroles.

Also, I am trying to set a relationship between users and security groups using the following code, but facing same issue as above:

List relatedIds = new List
{ securitygroupid };
req.module_name = “Users”;
req.module_id = userid;
req.link_field_name = “SecurityGroups”;

            req.name_value_list = new List<string>()
            {

            };
            req.related_ids = relatedIds;

Any help is appreciated.

Thanks