If you receive the "Library-in-apk_no_package_name" error when trying to install Fortnite on your Android device, first verify that your Android is compatible with Fortnite: What are the system requirements for Fortnite on Android?
Note: To check your system specifications, please see: How do I check the specifications of my Android device?
If your device is compatible, please can try the troubleshooting steps here: How do I troubleshoot crashes, errors, and performance issues in Fortnite on Android?