public void Configure(IServiceCollection services, IApplicationBuilder app, IHostingEnvironment env)
    {


        app.AddMvc().AddRazorPagesOptions(options =>
        {
            options.Conventions.AddPageRoute("/Products/Index", "");
        });

InvalidOperationException: No service for type 'Microsoft.Extensions.DependencyInjection.IServiceCollection' has been registered.

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().AddRazorPagesOptions(options =>
    {
        options.Conventions.AddPageRoute("/Products/Index", "");
    });
}