Open Chrome extension, Eventghost and CORS policy

I am unable to send join pushes to Eventghost. I have read of similar problems on this forum but I haven’t been able to resolve it. I should say that I have very limited IT skills.
My setup is:
Eventghost is on a Windows 10 Laptop
In Eventghost the Autoremote plugin port is set at 1818
Chrome extension is installed, the Eventghost port is also set at 1818. The Server IP/Host is left blank although I have also tried using the laptop’s IP.

Join is installed on several Android devices and Node Red.

If I send a join push to chrome the message gets through if I don’t have port 1818 entered on the chrome extension settings. When I enter port 1818 the message does not get through. Somewhere in the forum it was suggested that the Console in the Developers area of the extension may shed some light on the problem. This threw up:

join.html:1 Access to fetch at 'http://localhost:1818/push' from origin 'chrome-extension://flejfacjooompmlie………' 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. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

localhost:1818/push:1 Failed to load resource: net::ERR_FAILED

join.html:1 Uncaught (in promise) TypeError: Failed to fetch.

This is way above my abilities. Can anyone help?

Many Thanks

Sid