Panel cannot connect to API

Hello people,

I cannot access my panel. And I get the Error like those. Sorry, I have no idea what does it mean?

What sort of local setup are you using?

I use Gulp for localhost. Panel works for installation and first use. But second time I ran dev. I got this error and panel is not working anymore. I am not sure which part of my local setup should I show you.

  server: {
      enable: true,
      connect: {
        // For more options, see
        base: './src/',
        //open: true,
        router: 'kirby/router.php',

I haven’t change anything in .htaccess.

If I change lockhost:4000 to works. Probably problem in my setting?