Hi Tor,
There is a bug in the exercise that appeared recently. The resource group name in the code blocks doesn't get updated as it should. Please use instructions below to workaround the issue.
Please navigate to the Exercise - Design and implement IP addressing for Azure virtual networks, Activate a new sandbox, sign in, etc. Once sandbox is activated and black cloud shell window with "Welcome to Azure Cloud Shell" displayed, navigate to Plan IP addressing for your networks using the "Unit x of 6" dropdown above the exercise.
After page loads, immediately navigate back to Design and implement IP addressing for Azure virtual networks exercise. Once there, verify that the resource group name in the code blocks has been updated to something similar to learn-c95e635f-d291-8747-c339-12a8ef31691b instead of [sandbox resource group name]. Complete the exercise.
Please make sure you click the Copy button in upper right of each code block, right-click Paste into Cloud Shell window on right, then press Enter to execute command. Inspiration for above workaround came from @pnaroju's #2 suggestion in this post.
Please click Accept Answer and upvote if the above was helpful. If something is unclear add a comment below.
Thanks.
-TP