Ajax event on Grid row

I have a grid that has user privileges on it.

II want to be able to click the Y/N for each privilege on the row, and have Ajax event switch it (if its Y switch to No and vice versa)

Under Ajax events of this grid I select a field users.users_priv_att and made it an On Click event.
The two parameters to pass are also selected:
users.usersid and users.user_priv_att.

However, in the PHP code of the On Click event I cannot seem to retrieve these two variables

I have tried

$att = {users.user_priv_att};

$id = {users.usersid};

AND

$att =$_GET[‘users.user_priv_att’];
$id = $_GET[‘users.usersid’];
But nothing takes.
What am I doing wrong?
Is this even the proper approach?

The next line will be a PHP update of the field with

$new_att=‘N’;
if($att==‘N’)

{
$new_att=‘Y’;
}

$sql=" UPDATE users set user_priv_att = ‘$new_att’ WHERE usersid=’$id’ ";
sc_exec_sql($sql);