Somewhat recently I had to update to the 64 bit version of Raspbian OS to use Unifi Network 7.x. I had to use the tutorial linked from pimylifeup. Today the apt update switched to the 8.x branch of distribution and it said my architecture of armhf was not supported. To fix it, I just had to edit the file: /etc/apt/sources.list.d/100-ubnt-unifi.list from "arch=armhf" to "arch=arm64". If you were already running the latest 7.x then this should get you up and running. If you are upgrading from something older, visit the linked tutorial to get everything you need to be updated.