When using the API method host.get and there is an error regarding some parameter (for example "selectGroups") the following error message is returned:

Invalid parameter "/output": value must be "extend".

But as you can see in the request data there's no parameter "output":

{
  "jsonrpc": "2.0",
  "method": "host.get",
  "params": {
    "filter": {
      "hostid": [
        "10336"
      ]
    },
    "selectGroups": "groupid"
  },
  "id": 5
}

In fact the error is an invalid value for the parameter "selectGroups". This is misleading and makes it hard to find the cause for such an error.

Therefore this should be fixed so that the error messages really tell what's wrong. At least they shouldn't mention a wrong cause.