The Host Is Down error usually means that Screens is unable to reach the computer.
In almost all cases, this is caused by one of the following:
1. Your Device Isn't Connected to a Network
The iPhone, iPad, Vision Pro, or Mac you're connecting from must be connected to a network, either through Wi-Fi, Ethernet, or cellular (where applicable).
Things to check:
- Wi-Fi is enabled and connected.
- Airplane Mode is turned off.
- If you're using Ethernet on a Mac, verify the network cable is connected and the network is active.
- If you expect to connect to a computer on your local network, make sure both devices are connected to the same network.
2. Local Network Access Is Disabled
Apple requires apps to be granted permission before they can discover and communicate with devices on your local network.
If Local Network access is disabled for Screens, it won't be able to detect or connect to computers on your local network, even if both devices are connected to the same network.
For instructions on enabling Local Network access, consult this article.