I tried the same in my environment I got the same error like below:

Created app service and added outbound traffic vnet integration like below:

Vnet integration:


Ensure that virtual network allocated service endpoint Microsoft. Web
to allow traffic from your vnet network.


I have allow the my app service all outbound ip's and my local system public ip's
To allow all outbound Ip and local public Ip give address block 0.0.0.0/0
in access restriction this block will allow to access your Ip like below:

Now when I browse app service it's run successfully like below:

- Check that the appropriate subnet of the virtual network(vnet) is connected to your app service. The NSG rules might not be applied to the traffic if the app service is not connected to the appropriate subnet.
- For your app service, enable diagnostic logging to obtain more information about the request and possible issues or warnings that might help you identify the problem.