Hi Javier,
You should be able to work around the issue by first Activating the sandbox (solving puzzles, reviewing permissions, etc.) and then once you see the sign-in box appear on the right open a new browser tab. In this new tab, browse to https://shell.azure.com. If your existing sandbox hasn't expired you can use that instead of activating a new one.
When prompted, click Bash
Next choose No storage account required, for Subscription select Concierge Subscription, and click Apply.
After several seconds delay while a cloud shell is requested and connected to, you should see $ prompt. At this point you can complete the exercises instructions, copy/paste code from exercise tab to cloud shell tab as needed, etc.
NOTE: You need to complete tasks in Unit 3 Exercise - Create an Azure virtual machine and then jump to Unit 9 Exercise - Configure network access and complete the tasks there. Otherwise the Unit 9 exercise tasks will fail.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP