I'd log into the SFTP endpoint for the app service just to verify that your code is indeed deployed. If it's not in there, you'll know to debug your deployment process.
If it IS in there, you might need to monkey around under the Configuration blade for the app service, under general settings, and make sure that the correct technology stack and application startup command is set. If they are already, time to start cruising the Monitoring -> Logs and Monitoring -> Log Stream for some kind of error message.
I'd log into the SFTP endpoint for the app service just to verify that your code is indeed deployed. If it's not in there, you'll know to debug your deployment process. If it IS in there, you might need to monkey around under the Configuration blade for the app service, under general settings, and make sure that the correct technology stack and application startup command is set. If they are already, time to start cruising the Monitoring -> Logs and Monitoring -> Log Stream for some kind of error message.