CORS failure on local subnet

I have a local area test network 192.168.0.0/26.
On this there are three devices.

• nginx server 192.168.0.40 serving http://192.168.0.40/energy.html

• linux kde desktop 192.168.0.10 – chrome browser

• knx IP interface REST api 192.168.0.9

I have the following js code on the nginx server:

fetch("http://192.168.0.9/baos/GetDatapointValue?DatapointStart=161&DatapointCount=89&Format=Default")
.then(response => console.log(response))
.catch(error => console.log(error));

This fails with a CORS error –
*
Access to fetch at ‘http://192.168.0.9/baos/GetDatapointValue?DatapointStart=161&DatapointCount=4&Format=Default’ from origin ‘http://192.168.0.40’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. If an opaque response serves your needs, set the request’s mode to ‘no-cors’ to fetch the resource with CORS disabled.*

I would expect a json responce with the knx data.
{
  "Result": true,
  "Service": "GetDatapointValue",
  "Data": [
    {
      "Datapoint": 161,
      "Format": "DPT5",
      "Length": 1,
      "State": 16,
      "Value": 4
    },
    {
      "Datapoint": 162,
      "Format": "DPT5",
      "Length": 1,
      "State": 16,
      "Value": 4
    },
    {
      "Datapoint": 163,
      "Format": "DPT5",
      "Length": 1,
      "State": 16,
      "Value": 4
    },
    {
      "Datapoint": 164,
      "Format": "DPT5",
      "Length": 1,
      "State": 16,
      "Value": 4
    }
  ]
}

If I paste the fetch URL into the browser – this works.
But the js script gives the CORS error.
I think that the schema, the address, and the port are the same so cannot see why I get the CORS error.

Many thanks for any help here