This is my first time using this plugin so there is a good chance this is user error.

I've read the docs, and installed as instructed.
I've got a valid json config 

{
  "Wipe data on new map": true,
  "Permission cache time (seconds, 0 to disable)": 0,
  "Permissions": [{
      "Permission": "entitylimit.default",
      "Priority": 1,
      "Limits": {
        "sleepingbag_leather_deployed": 2
      }
    },
    {
      "Permission": "entitylimit.vip",
      "Priority": 2,
      "Limits": {
        "You can get shortnames at http://bit.ly/orange_entities": 0,
        "foundation": 20,
        "cupboard.tool.deployed": 5,
        "wall": 35,
        "wall.doorway": 5,
        "door.hinged.metal": 5
      }
    },
    {
      "Permission": "entitylimit.top",
      "Priority": 999,
      "Limits": {
        "You can get shortnames at http://bit.ly/orange_entities": 0,
        "foundation": 20,
        "cupboard.tool.deployed": 5,
        "wall": 35,
        "wall.doorway": 5,
        "door.hinged.metal": 5
      }
    }
  ]​

I verify the the connected user has default permissions in the console and they do, so in theory they should not be able to place more than 2 sleeping bags, yet they can place as many as they want. 
I get no error or warnings 

Is there something basic I have to do that I've missed ?

I have 2 other plugins working (very basic a banner message and a smelting change plugin so I know umod/oxide is working fine).

Appreciate any inputs on this.