This should be just used as basic approach on how you can support busy on busy.
First you can check if the new APPLICATION was installed correctly:
The newly created appliance will be loaded during the Frontend server startup procedure and you will be able seeing a not in Event 30253, indicating the application was included in the loading process.
Here you will find a pre-defined set towards busy on busy.
Generally busy on busy messages look like this example below:
Good luck troubleshooting....
Author: Thomas Poett MVP, Business Unit Lead Microsoft Unified Communication