The ExpressVPN browser extension is not yet supported on Safari 12.
Only Safari Extensions distributed within Apple’s Safari Extensions Gallery were supported at the launch of Safari 12. Legacy extensions outside the gallery, including the ExpressVPN extension, are not yet compatible.
Please consider using the Chrome or Firefox browsers with their accompanying ExpressVPN extensions while we work on a new version of the ExpressVPN Safari extension.
Note: The ExpressVPN browser extension is not necessary for the VPN service to work, but it allows you to control the VPN app from within the browser while also conferring location anonymity.
For further assistance, please contact the ExpressVPN Support Team.