Can't get apitester working

Your software
My Mautic version is:v3.2.1
My PHP version is: 7.3.19-1~deb10u1
My Database type and version is: MariaDB 10.3.27

Your problem
I installed api-tester from github ( doing download and unzip method (put all files from repo into /lib folder. When i try to access the tester by i get this JSON error response in my browser:
{“errors”:[{“message”:“API authorization denied.”,“code”:401,“type”:“access_denied”}]}
So i guess, even for the tester i need to provide some credentials. I turned basic auth on (for testing) but still no login dialog appears. Maybe there are some URL-params needed to use this?

These errors are showing in the log:

Steps I have tried to fix the problem:
clearing the cache