Since macOS High Sierra 10.13, Apple has introduced a new security feature that requires user approval before installing new third-party drivers.
When installing Systemwide for the first time on macOS High Sierra or later, a pop-up (similar to the screenshot below) will appear. If you see a "System Extension Blocked" error message please click OK. You will then need to ‘allow’ the driver installation process to complete from the ‘security & privacy’ settings in System Preferences” - please see the instructions set out in steps 1-4 below.
Please make the following changes to your Security & Privacy settings to enable the system extension:
1) Open System Preferences, click on Security & Privacy.
2) You will see a message: System software from developer "Sonarworks SIA" was blocked from loading.
3) Click: Allow.
You may need to click the Lock symbol in the bottom right corner of your Security & Privacy menu to make this change.
4) After clicking "Allow", restart the installer and it should now complete without errors.