there is no plus button to add devices
Hi Michael,
Thank you for reaching us with your concerns. We have removed AVG Zen (management console) from Internet Security interface and activation via invitation code may not work.
We request you to follow the normal installation procedures performed on first device. Else, refer this article: http://support.avg.com/SupportArticleView?urlname=Download-and-install-AVG-Ultimate to download and install it.
We are here if you need further help.