Hi,
There is currently an issue with the sandbox for that module which is why it just shows 99% or some sort of error with retry button.
To work around the issue, please open a new browser tab and navigate to below link:
Solve puzzle(s), review/accept permissions, etc., and wait for window on right side to show Welcome to Azure Cloud Shell. Next leave that tab open, and click on the exercise browser tab you were on and complete the instructions.
I tested and was able to create storage account as described in the instructions without any issues using above workaround.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP