RestAPI Cors Problem

I'm building a Flutter app for smartphones and with same code a Flutter web app.

Both are using IRIS with a RestAPI.

As described in your documentation

• https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=GR... 

I added

in the Info block of the Swagger definition and added

• Parameter HandleCorsRequest = 1;

in the spec file after generating the RestAPI.

I also copied the example dispatch class to

With the Android app on my smartphone the OnHandleCorsRequest() is called although the cors data are not set by the request and handling a cors request is not needed. I can see this by setting a global in this method showing the %request.CgiEnvs sent by the app. The data access from the app to IRIS is working as expected.

But in Flutter Web I always get the Cors Error:

• Access to XMLHttpRequest at 'http://solidara.net:52773/csp/solidara/get/solidara' from origin 'http://app.solidara.net' has been blocked by CORS policy:
• Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

and the OnHandleCorsRequest() is not called at all by IRIS!

Any idea, what's going wrong here?