For the past week, I couldn't update Nutyx's package manager. I just use it in a virtual machine and update it occasionally. So to update Nutyx, you need to run: 
sudo cards sync && sudo cards upgrade. 
While the cards package manager would sync, I kept getting the same error: which was a download error for a newer version of the package manager, cards. So, I decided to read the fine manual for cards. 
man cards
In there it said you could build a package from ports, blah, blah, blah. And so I ran:
sudo cards install -u cards
and that worked! I could then proceed to upgrade Nutyx.