App Store Error
iMac (21.5-inch, Late 2012), macOS Sierra (10.12.6)
Hello and welcome to Apple Support Communities, paul214264.
If I understand your post correctly, you are getting an error when trying to update through the App Store on your Mac. I'd like to help.
Try the steps in this article:
If you can't connect to the iTunes Store, iBooks Store, or App Store
Let us know if that resolves this issue for you.
Thanks for using the Apple Support Communities. Take care.
App Store Error