SPA developement with a local proxy to server apis is a common technique nowadays. Here's a usefull method to debug proxy if you need to find out why your proxy fail.

  defineConfig(mode => {
  
    return {
      server: {
        proxy: {
          // ...proxy config here
        },
        configure: (proxy, _options) => {
          proxy.on('error', (err, _req, _res) => {
            console.log('proxy error', err);
          });
          proxy.on('proxyReq', (proxyReq, req, _res) => {
            console.log('Sending Request to the Target:', req.method, req.url);
          });
          proxy.on('proxyRes', (proxyRes, req, _res) => {
            console.log('Received Response from the Target:', proxyRes.statusCode, req.url);
          });
        },
      },
    };
  });