@San Sanych
To change the background sound to a custom option, you would typically need to check if the API supports custom background sounds. If it does, you would follow the API's documentation to upload or specify your custom sound file.
Regarding the issue with the "office" sound having an unnatural ending, I would recommend providing feedback to the API provider so they can improve the sound file. If there's an option to adjust the sound settings or choose a different preset that better fits your needs, you could try that as well.
If you need assistance with changing the background sound or reporting the issue with the "office" sound, please let me know, and I can guide you through the process or escalate the issue to the appropriate support team.