If you've installed a Line 6 driver and the device will not subsequently connect, it is possible that the driver is disabled by the system.
How to check if the software is disabled by the system:
• Click on the Apple symbol in top-left corner of the screen and go to "About this Mac -> Overview ->System Information -> Disabled Software”.
• If there is disabled software, it will be presented with a 10-digit software ID and a file descriptor, similar to "VCN535JA6Y - com.line6.driver.xtaudio"
• Take a screen shot or write down the ID (in this example it’s VCN535JA6Y – yours might be different).
How to enable software that is disabled by the system:
• Uninstall the drivers: https://line6.com/support/page/kb/recording/computer-audio-set-up-and-troubleshooting/how-to-uninstall-line-6-drivers-from-mac-osx-r85/
• Reboot to recovery, holding down Command-R while restarting.
• From Menu -> Utilities, open Terminal and type the following (replacing the system ID with yours):
“spctl kext-consent disable”
“spctl kext-consent add VCN535JA6Y" (replace the VCN535JA6Y with yours if different)
“spctl kext-consent enable"
• Reinstall the driver.
• Open System Preferences -> Line6 Audio-Midi devices and plug the device into the Mac. The device should appear in a few seconds.