Beatbox project help

Hi all,
I am currently attempting the beatbox challenge.

https://www.codecademy.com/paths/create-a-back-end-app-with-javascript/tracks/bapi-javascript-arrays-loops-and-iterators/modules/project-beat-mix/informationals/bapi-p2-beat-mix

when i run npm start server it start it all right on port 4001… but when i go to 127.0.0.1:4001 all it returns is “Cannot GET /” I’ve tried it with chromium brower version:
Version 76.0.3809.100 (Official Build) Built on Ubuntu , running on LinuxMint 18.3 (64-bit)

also with firefox: 68.0.1

any help appreciated.