CORS error: set the request's mode to 'no-cors' to fetch the resource with CORS disabled

Below is my code for reference in startup file.

Configureservice:
services.AddCors(options =>
{
options.AddPolicy("AllowAll",
builder =>
{
builder.WithOrigins("https://webapp.io/", "https://www.webapp.io/")
.SetIsOriginAllowed((host) => true)
.AllowAnyHeader()
.AllowAnyMethod();
});
});
//CORS

services.AddControllers();


Configure:
public async void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
//var builder = new Microsoft.Extensions.Configuration.ConfigurationBuilder();
//builder.SetBasePath(env.ContentRootPath)
// .AddJsonFile("configuration.json", optional: false, reloadOnChange: true)
// .AddEnvironmentVariables();

//Configuration = builder.Build();
//CORS
//app.UseCors(builder => builder.AllowAnyHeader().AllowAnyMethod().SetIsOriginAllowed((host) => true).AllowCredentials());
app.UseCors("AllowAll");
app.UseMiddleware<corsmiddleware>();
// END CORS

await app.UseOcelot();
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();

app.UseEndpoints(endpoints =>
{
endpoints.MapControllers();
});
loggerFactory.AddLog4Net();
}
}