Hi Vadym Skliarov,
Thanks for reaching out to us on Microsoft Q&A forum.
We are sorry to hear that you are experiencing issues in running training scripts in the sandbox.
Before activating the Sandbox kindly follow the troubleshooting steps as mentioned below for the issue:
Step 1: Sign-out from all the tabs in the current browser and clear the cache files and try login again with your learn ID credentials.
Step 2: Sign-out from current browser login and try to login from an incognito window/in-private window.
Step 3: Switch to a different browser and try login again.
After completing the troubleshooting steps kindly activate a new sandbox by clicking the "Activate sandbox" button for an exercise. Upon activating a sandbox, a default subscription named "Concierge subscription" is generated for the Microsoft Learn Sandbox directory along with a default resource group name starting with learn.
Note: Kindly do not delete any resource groups, the sandbox automatically cleans up your resources when you're finished working with any module.
If you are still running into issues, kindly attach the screenshots of the error you are getting. We will be glad to assist you.
If the information is helpful, please Accept Answer & Upvote so that it would be helpful to other community members.