StartupGraphQL.cs

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseDefaultFiles();
            app.UseStaticFiles();
            app.UseWebSockets();
            app.UseGraphQLWebSocket<OrdersSchema>(new GraphQLWebSocketsOptions());
            app.UseGraphQLHttp<OrdersSchema>(new GraphQLHttpOptions());
            app.Map("/schema.graphql", config => config.UseMiddleware<SchemaMiddleware>());
}