macOS 10.13 and 10.14 require that system extensions are manually approved before they can be loaded. Viscosity uses a system extension on these versions of macOS to allow TAP (bridged) VPN connections to be created. Viscosity does not use a system extension on macOS 10.15 and later: this article only applies to macOS 10.13 and 10.14.

If you attempt to connect to a VPN connection in Viscosity that uses TAP, and the extension has not been approved, you may receive the following alert from macOS, as well as an alert from Viscosity.

To resolve the issue, click the "Open System Preferences" button in Viscosity's alert to be automatically taken to the necessary section in System Preferences. You can also get to this section manually by going to the Apple menu, selecting "System Preferences", and clicking on the "Security & Privacy" icon.

You should see a message similar to "System software from developer SparkLabs Pty Ltd was blocked from loading". Click the "Allow" button next to this message to allow the TAP system extension to load.

If the Allow button is disabled, you may need to click on the padlock icon and enter the username and password of an administrator account. If the message is not listed, you may need to attempt to connect your TAP connection in Viscosity, and the open System Preferences again.

For enterprise environments, a Kernel Extension Policy can be set to allow the TAP extension to load without needing user approval. For more information please refer to Apple's documentation. Alternatively deployments can be updated to macOS 10.15 or later, in which case the TAP extension is no longer required.