i have edited the config and was able to modify decay rates for the twig, wood, stone, metal, hqm and those are working but the problem is that decay is not working for the items under other multipliers i am attaching my config here and also i have given the permission only after that the decay was working for the twig,etc build levels.

here is the config

{
  "General": {
    "Disable decay for all entities": false,
    "Exclude \"Other Multipliers\"": false,
    "Use permission": true,
    "Decay if there is no owner (and perms enabled)": false,
    "Permission": "nodecay.use",
    "Output": {
      "Output to server console": false,
      "Log to file": true,
      "Log file name": "NoDecay-Log"
    },
    "Cupboard Settings": {
      "Disable No Decay if resources placed in TC": false,
      "Require Tool Cupboard": false,
      "Any authed on TC": false,
      "Cupboard Range": 30.0,
      "Block cupboard wood": false,
      "Block cupboard stone": false,
      "Block cupbard metal": false,
      "Block cupboard high quality": false
    }
  },
  "Building grade multipliers": {
    "Twig multiplier": 4.0,
    "Wood multiplier": 4.0,
    "Stone multiplier": 4.0,
    "Sheet Metal multiplier": 3.2,
    "Armoured multiplier": 2.4
  },
  "Other multipliers": {
    "wall.external.high.stone": 480.0
  }
}