How to Troubleshoot the Auto Scale

I've set up the Auto Scale logic app per https://docs.microsoft.com/en-us/azure/virtual-desktop/virtual-desktop-fall-2019/set-up-scaling-script#create-the-azure-logic-app-and-execution-schedule and am getting the following Exception each time the runbook runs.

You cannot call a method on a null-valued expression. (You cannot call a method on a null-valued expression.)

How do I determine the issue? I don't see a way to step through the logic app and determine what is a null value.

Thanks.