Hi Panda_lover1,
We appreciate you reaching out to us.
We’d like to gather additional details that may help us be in a better position to assist you.
Are you able to play your music or audiobook when playing other games?
Let’s start by checking for a software update and make sure that you are running the latest version of iOS.
While it isn't inherently assured that an update will resolve the issue, updating to the latest software version for your device can help isolate potential software issues.
Kindly secure a backup and update.
- How to back up your iPhone, iPad, and iPod touch - Apple Support
- Update your iPhone or iPad - Apple Support
Also, check for app updates for Roblox. You can use the article below as a reference.
How to manually update apps on your Apple device - Apple Support
If the behavior persists, you may have to get in touch with the app developer of Roblox.
Their app may have a setting that may allow you to play music or audiobook in the background
You can use the article below to help you in reaching out to them.
How to contact an app developer - Apple Support
Take care!