seems i am experiencing this issue as well, i created a new instance of the azure blockchain workbench and successfully deployed it. I open the app service URL xendbw-x3wznf.. copied the cloud shell command and pasted it on the cloud shell with the following output:
abayomi@Azure:~$ cd; Invoke-WebRequest -Uri https://aka.ms/workbenchAADSetupScript -OutFile workbenchAADSetupScript.ps1; ./workbenchAADSetupScript.ps1 -SubscriptionID 29420446-f530-4754-b3a1-5c88833266f5 -ResourceGroupName xendwb -DeploymentId x3wznf
bash: Invoke-WebRequest: command not found
bash: ./workbenchAADSetupScript.ps1: No such file or directory
mind you during the creation process i chose an exiting blockchain network which also deployed successfully as PoA network.
you help will be greatly appreciated,