How to add user to SharePoint group using REST & SPServices

Using REST:-

function AddUserToSPGroup()
{
var vCurrentLoggedUser2=$().SPServices.SPGetCurrentUser({fieldName: "UserName",debug: false});

vCurrentLoggedUser2= "KL\\" + vCurrentLoggedUser2;
var requestUri = _spPageContextInfo.webAbsoluteUrl + "/_api/web/sitegroups(57)/users";
$.ajax({
url: requestUri,
type: "POST",
data: JSON.stringify({'__metadata': { 'type': 'SP.User' }, 'LoginName': vCurrentLoggedUser2}),
headers:
{
"accept":"application/json;odata=verbose",
"content-type": "application/json;odata=verbose",
"X-RequestDigest":$("#__REQUESTDIGEST").val()
},
success: onSuccess,
error: onError
});//End of ajax
function onSuccess(data)
{
alert('User Added');
}
function onError(error)
{
alert(JSON.stringify(error));
}
}

Using SPServices:-

function SetContributeAccess()
{
var vCurrentLoggedUser=$().SPServices.SPGetCurrentUser({fieldName: "Title",debug: false});

$().SPServices({
   operation: "AddUserToGroup",
   groupName: "Users",
   userLoginName: vCurrentLoggedUser,
   async: false,
   completefunc: function(data,status){
      alert("User added to group");
   }// End of completefunc
}); //End  of SPServices
}//End of SetContributeAccess