Failed to call hook 'cmdRun' on plugin 'Npctp v2.4.6' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Npctp.cmdRun (ConsoleSystem+Arg arg) [0x00507] in :0
  at Oxide.Plugins.Npctp.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00802] in :0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

Oke I want to make the guard open a door, it does take the hv 556 from me as already preset.

the Economics settings doesnt take the money from the balance and the npc doesnt open the door.

In plugin.cs settings I putted every Economic setting from false to true, and here is the npc settings:

{
  "NpcTP": {
    "2038854755": {
      "NpcName": "<color=orange>Npc</color> : ",
      "SpawnFile": null,
      "Cooldown": 1,
      "CanUse": true,
      "useUI": false,
      "Cost": 10000.0,
      "permission": "npctp.default",
      "useItem": true,
      "ItemShortName": "ammo.rifle.hv",
      "ItemAmount": 1,
      "UseCommand": false,
      "CommandOnPlayer": false,
      "Command": "say",
      "Arrangements": "this is a test",
      "useMessage": true,
      "MessageNpc": "Pay your duties to enter this castle!",
      "EnableDead": false,
      "DeadOnPlayer": false,
      "DeadCmd": "jail.send",
      "DeadArgs": "5",
      "OpenDoor": true,
      "DoorLocX": 531.444336,
      "DoorLocY": 7.316393,
      "DoorLocZ": -264.448181,
      "DoorId": 0,
      "NoPermKill": false,
      "KillSleep": false
    }
  }
}

The Npc gives me also feedback that it took the item from me, and that works all perfect

Thanks! With your help I figured it out!

The door I didnt look at, and dit it now over by looking at it, economics was set to true in the plugin and npc but not the config.

When this was set to true, the money went off! 

But the hook error then still presisted and the door didnt open. So I looked further, and saw this message:

"[Npctp] Spawns Database could not be found you only can use command NPC or random spawns!"

So installed this mod and it works perfect now! Thanks m8! Awesome mod ^^