Cors Error on build your own Analytics dashboard

I’ve recently been testing the offical template of Build your own Analytics dashboard and it doesn’t work.

I tell you the errors to see if someone can help me.

  1. Utils.js doesn’t exist anymore, luckily I found it. (“Fixed”)

  2. Cors problem that I am not able to solve!

I dont know how ti fix that, i tried like 10 solutions and i readed some docs, and still nothing.
Thanks in advance

The docs is the following, i cant post link!