CORS problem with PUT and DELETE

Hi,

I am developing an API that needs to use PUT and DELETE Verbs for actions in several controllers. But on each of these CORS is rejecting them despite being set up for any Origins, any Methods, any Headers, etc. My CORS policy is set up near the top of ConfigureServices/Startup.cs as follows:

       services.AddCors(options => options.AddPolicy("CorsPolicy", builder =>  
        {  
            builder  
                .AllowAnyMethod()  
                .AllowAnyHeader()  
                .AllowCredentials()  
                .SetPreflightMaxAge(TimeSpan.FromSeconds(2520))  
                .SetIsOriginAllowed(origin => _ = true);  
        }));  

And in Configure I have:

        app.UseCors("CorsPolicy");  

I have applied these to all the relevant controllers with these attributes:

[EnableCors("CorsPolicy")]   

But I am still getting these CORS errors:

I have followed suggestions I found elsewhere and even included API calls for OPTIONS in two of my controllers, as I do understand that this is likely to be related to OPTIONS requests associated with the PUT and DELETE verbs from the Front End Browser. Likewise I included the .SetPreflightMaxAge(TimeSpan.FromSeconds(2520))
option in my setup.

But it has not eliminated the problem. Can anyone see what I am doing wrong?

Thanks

Ian