Hi there Adam O'Neil
Thanks fore using QandA platform,
Guess you are using Free trial account.
Create an App Service app, or use an app that you created for another tutorial. The app should be in an Azure Public region. At this time, Azure National Clouds are not supported.
To use an App Service domain, the app's App Service plan must be a paid tier and not Free (F1). See Scale up an app to update the tier.
Remove the spending limit on your subscription. for more info follow the below documentation.
If this helps kindly accept the answer thanks much.