Hello Theresa,
Did you follow the steps as mentioned in this article to activate AVG Internet Security subscription on Mac?
I have a Mac and a dell laptops my MacBook Air has avg free on it but it will not allow me to upgrade to internet security I bought the avg internet security for multiple devices and it covers up to 5 devices for up to 1 year I was able to to upgrade on my dell laptop and on my android phone to pro without a problem with the same activation key
Hello Theresa,
Did you follow the steps as mentioned in this article to activate AVG Internet Security subscription on Mac?