I just downloaded the Astroprint onto a Rasberry Pi 3 Model B with a USB WIFI Dongle and I can find my printer if I am on the Hotspot but not if I go through the Astroprint Cloud. I like the ability of Astroprint because I want to do timelapses.
Please Help
Welcome to AstroPrint! 
In order to see your astrobox in your cloud account, you have to first PAIR IT with the cloud.
In order to do that, go to your LOCAL ASTROBOX SETTINGS and click on the ROCKET ICON on the top right hand corner.
This will prompt you to login to your cloud account.
After you login, the rocket will turn GREEN.
Now, your Astrobox is paired with the cloud.
Just login to your cloud account and click on the MONITOR APP, and you are all set.
Got it?
All the icons on the LOCAL Astrobox should be green like this:
My problem is when I access my astroprint through the hotspot it creates, it says that “Astroprint.com can’t be reached”
Is your local AstroBox connected to the Internet?
Is it via Ethernet or WiFi?
Are you behind a firewall or a router with restrictive settings?
Because AstroPrint.com is up — which means, you have a connectivity issue FROM your box TO AstroPrint.