@Sree Bandaru Thanks for reaching out. In case if you have VNET integrated either at the function app end or azure service bus end or the client/service bus in under the restricted network or if there is configuration issue then you could observe the error where the application is not able to communicate with the service bus.
If your client application is under the virtual network/no internet access is there so you should enable private endpoint as the communication can happen via the private endpoint.