I have resolved the issue.
The issue is being caused by an Azure Access Restriction (i.e. Azure Web App Firewall) that was applied to both the API and Identity Server web apps. We had an Access Restriction on the Sites so that they could only be accessed from our corporate network. It's only because I noticed in maliming posts that there was a 403 Forbidden Error that I decided to remove the Access Restriction to help with resolving this Support Issue. Now I just need to figure out what Firewall Rule is required to let Identity Server work.
Thanks maliming and gterdem for your help