I have been having the same issue for the past 24 hours. Spoken to 3 different representatives and the still has not been resolved. I have MacOS High Sierra on my Macbook Air 2017. I am trying to download to the Monterrey software, but my laptop won't even let me install it. It keeps showing Checking "null". Even when I tried installing Big Surr, it doesn't work. Please tell me there is a solution for this!