Hi,
Did you click Activate Sandbox, Review Permissions, then click Accept when prompted? After that, it should've finished creating the sandbox and then show time remaining (it is valid for 4 hours).
Below is the link to open the Azure portal to concierge subscription (you need to sign in using same credentials you are using for MS Learn):
https://portal.azure.com/learn.docs.microsoft.com
Please let us know at what point the process is failing.
Thanks.
-TP