Troubleshooting#

Find what you are seeing, then check and fix it in the order given. Messages in quotes are exactly what the app on the device or the host window on the PC shows. Both follow your language setting, so they may appear in Japanese instead.

If your problem is not here, look at Known issues, and then tell us.

Start here: the host checks itself#

On the PC, open the host window (the tray icon) and go to the Connection tab. The first section, Readiness, checks the PC side for you. When everything is in order it reads Ready. When something is not, it opens the line that failed and says what to do:

Show details (bottom left) shows all seven lines even when they pass. A screenshot with it on is also what helps most when you report a problem.

Symptoms#

Finding the PC

• The app says "No hosts found yet"
• On public Wi-Fi
• A VPN is on
• The PC has more than one network adapter
• "Could not reach the host"

Connecting

• The host asks for a pairing PIN
• "The certificate of the host is not the one that was expected"
• "A different host answered here"
• "Its certificate fingerprint is unknown"
• "The host has reached its connection limit"
• "This host requires encrypted connections"
• "Could not open the receive ports"

While streaming

• "The connection dropped. Reconnecting…"
• "The host is not responding"
• The picture does not arrive, or breaks into blocks
• The tablet shows a copy of the PC's screen
• No sound on the device
• A drawing app ignores the pen
• HDR does not come through
• The camera does not work

On the PC

• The installer is blocked or will not install
• No virtual display can be created
• Closing the window did not quit PrismDesk
• Activating Pro fails
• "Could not check for updates"

Finding the PC#

The app says "No hosts found yet"#

1. Is PrismDesk running on the PC? Look for the tray icon. In the host window, the button at the bottom left should read Stop the host; if it reads Start the host, press it.
2. Are both on the same network? Same router, same subnet. A guest SSID, AP isolation, or a router that keeps its 2.4 GHz and 5 GHz networks apart all hide the PC.
3. Look at Readiness on the host's Connection tab (above). A missing firewall rule hides the PC the same way a wrong network does.
4. Connect without discovery. The host's Connection tab shows a QR code and a connection string. In the app, tap Scan a QR code, or open Other ways to connect (address, USB) → Enter a host directly and paste the string.

The search keeps running while that screen is open; a host appears as soon as it answers. More in Set up over Wi-Fi.

On public Wi-Fi#

Hotel and café Wi-Fi often stops devices from reaching each other, so the PC is never found. Turn on Mobile hotspot on the PC (Windows Settings → Network & internet) and connect the device to it. The app marks a host reached this way as Hotspot. Pick the 5 GHz band if the PC offers it; the hotspot uses more of the PC's battery.

A VPN is on#

A VPN on the PC or on the device can hide the PC from discovery, and can also make a found PC impossible to connect to.

• The PC is not found. Discovery does not cross a VPN. Paste the connection string from the host's Connection tab into Enter a host directly. Once you have connected, the app remembers the host.
• The PC is found, but connecting fails. The VPN is sending traffic for your local network into the tunnel. Let the VPN leave your local network alone (the setting is often called exclude private IPs, allow LAN access or local network sharing), exclude the PrismDesk app from the VPN, or turn the VPN off. We hit this with WireGuard during development; it is a VPN setting, not something PrismDesk can change.

The PC has more than one network adapter#

A VPN adapter, a virtual machine network or a second network card all count. The host's Connection tab then says "There are 2 adapters. Pick the one on the same network as the device…" and lists Addresses of this host. Press Use next to the one on the same network as the device. The QR code and the connection string change with your choice. Prefer USB (recommended) when it is listed.

"Could not reach the host"#

The full message is "Could not reach the host. Check that PrismDesk is running there and that both are on the same network." Go through No hosts found yet — the causes are the same.

If it says "The host is not answering. The connection went through, but nothing came back." instead, the PC was reached but did not finish the connection: look at Readiness on the host, and at the Log tab for a line in red.

Connecting#

The host asks for a pairing PIN#

You see "A pairing PIN is required." or "The pairing PIN does not match."

The PIN is the six digits shown on the host's Connection tab, to the right of the QR code. Type it into Pairing PIN (6 digits) and press Reconnect with this PIN. Scanning the QR code fills it in for you, and the app remembers it for next time.

If it keeps failing, someone may have pressed Generate a new PIN on the host (Settings → Security): read the PIN on the PC again. After several wrong PINs, the host turns down every PIN from that device for a while — even the right one still reads "does not match". Wait a little, then try again.

If the app warns "This connection is not encrypted. The PIN will be sent in a form that anyone on the same network can read.", encryption is turned off on the host. Turn it on under Settings → Security → Encrypt the traffic and start the host again, rather than sending the PIN in the clear.

"The certificate of the host is not the one that was expected"#

The device remembers each PC by its certificate. This message means the PC at that address now has a different one. Either:

• You replaced the certificate on the PC (Settings → Security → Replace the certificate — the button is shown only with Show details on and encryption on), or reinstalled in a way that made a new one. Scan the QR code on the host again, and enter the PIN again if asked.
• It is a different PC, or something on the network is pretending to be yours. Do not connect. Check that you are on your own network.

"A different host answered here"#

A host with a different certificate answered at a saved address, often because the router gave the address to another PC. Connect from that host's own line in the list. If you replaced the certificate on your PC, scan its QR code again.

"Its certificate fingerprint is unknown"#

The full message is "This host encrypts its traffic, but its certificate fingerprint is unknown. Use the QR code or the connection string shown on the Connection tab of the host." Do exactly that: the QR code and the connection string both carry the fingerprint.

"The host has reached its connection limit"#

The host already has as many devices connected as it allows. The free edition connects one device at a time; Pro connects up to four. Disconnect one of the other devices (in its app, or with Disconnect on the host's Connection tab), then connect again.

"This host requires encrypted connections"#

The full message is "This host requires encrypted connections. Update the app on this device." The app is older than the host. Update it from Google Play.

"Could not open the receive ports"#

The full message is "Could not open the receive ports (…). Another app may be using them, or a previous session is still holding them. Restart the app." Close the PrismDesk app completely (swipe it away from recent apps) and open it again.

While streaming#

"The connection dropped. Reconnecting…"#

The app reconnects by itself, and after a short drop the session continues on the same virtual display. If it gives up with "Could not reconnect to the host", press Try again or connect from the list.

If the connection was gone for longer, a new session starts and Windows builds the virtual display again. Windows that were on it can come back on the main monitor; move them back.

Drops that keep happening point at the network: 2.4 GHz Wi-Fi, a weak signal, or a busy channel. The app itself says "2.4 GHz Wi-Fi drops out easily. 5 GHz is recommended."

"The host is not responding"#

The picture goes black with "The host is not responding" and the time since the last data. Nothing has arrived from the PC for a few seconds. That can be the PC going to sleep, the host being stopped, or the network dropping out for a moment — the device cannot tell which.

"The picture comes back on its own if the host returns." If the PC is asleep, wake it; nothing needs doing on the device. To stop waiting, press Open controls and choose Disconnect.

The picture does not arrive, or breaks into blocks#

• Stuck on "Waiting for the picture…" while the PC's screen is off. We have seen the virtual display stop producing frames while the PC's own monitor was turned off by power settings. Move the mouse or press a key on the PC to wake its screen.
• The picture breaks into blocks and stays that way. On the host's Connection tab, press Redraw the screen. That resends a complete picture.
• "The decoder could not be started" on the device. The message names the codec and size it tried. Try the app's Settings → Codec → H.264, or a smaller Virtual display resolution, and connect again.

The tablet shows a copy of the PC's screen#

You wanted a second desktop, but the tablet shows the same thing as a PC monitor. Windows has switched the virtual display to Duplicate these displays. The host says so on its Statistics and Log tabs.

• Check that Always keep the virtual display extended (host Settings → Virtual display) is still on — it is on unless someone turned it off — or
• In Windows Settings → System → Display, choose Extend these displays.

If you chose Mirror in the app on purpose, that is what Mirror does; switch the app's Settings → Display mode to Extend.

No sound on the device#

• Audio is decided before connecting. In the app, check Settings → Audio, and connect again. It cannot be switched during a session.
• Is anything playing on Windows? The host's Statistics tab says "Audio: idle (nothing is playing on Windows)" when there is nothing to send — that is not a fault.
• "Silent: audio is being sent, but it is all zeros. Check the playback device on Windows" — Windows is playing to a device PrismDesk is not listening to, or you have just switched the playback device. Check the playback device in Windows sound settings.

A drawing app ignores the pen#

Set the app's tablet input to Windows Ink instead of WinTab. Exact steps for Krita are in Pen. The device also says so the first time the pen touches: "Pen input received. If your drawing app ignores the pen, set its tablet input to Windows Ink."

HDR does not come through#

After connecting, the app lists what the host changed and why. Find the reason here:

HDR arrives but looks like SDR. Some panels cannot get brighter than SDR; the app says so under Color space. See HDR. To check what is really being sent, turn on Show details on the host and read HDR as measured on the Connection tab.

The camera does not work#

• "Using the device camera as a webcam is part of PrismDesk Pro." The camera needs Pro on the PC.
• No Camera button on the device. Check that Publish the camera of the device as a Windows virtual camera (host Settings → Virtual camera) is still on — it is on unless someone turned it off.
• "Camera permission has not been granted." Press Open app settings and allow the camera for PrismDesk.
• PrismDesk Camera is not in an app's camera list. Close that app and open it again — apps read the camera list when they start. More in Webcam.
• The Windows Camera app cannot save photos (0xA00F424F). That is a Windows library problem, not the camera. The fix is on the Webcam page (Photos will not save).

On the PC#

The installer is blocked or will not install#

• "Windows protected your PC". See SmartScreen for what to check before you press Run anyway.
• It stops on Windows 10. PrismDesk needs Windows 11 (build 22000 or later). This is deliberate.
• "The virtual display driver could not be installed." The reason is in setup.log in the PrismDesk folder, which the message names. Run the installer again; if the same message comes back, report it with that file.
• "The firewall rules could not be added." PrismDesk still installs, but Windows may ask whether to allow it the first time a device connects — say yes. Running the installer again retries the rules.
• "Windows does not trust whoever signed the PrismDesk display driver" (0x800B0109). The installer you have is not a release build. Download the installer from the Releases page.

No virtual display can be created#

• "The driver is not installed, so no virtual display can be created. Run the PrismDesk installer again." Do that.
• "Could not create the virtual display device (no administrator rights)." PrismDesk needs administrator rights to create a display. Start it from the Start menu and accept the Windows prompt, or let the sign-in start-up entry start it.
• Readiness says "the driver is not responding. Restart the PC". Restart the PC. We have seen this after the PC's own monitor was turned off while a device was connected.

Closing the window did not quit PrismDesk#

That is on purpose: closing the window leaves PrismDesk in the tray, still listening for devices. To quit, right-click the tray icon → Exit.

Activating Pro fails#

For anything about an order, write to [email protected] rather than a public issue.

"Could not check for updates"#

The full message is "Could not check for updates. Check that this PC is connected to the internet." Check for updates fetches one small file from https://prismdesk.app when you press it, and nothing else. The latest version is always on the Releases page.

Reporting a problem#

Two things make a report useful: the diagnostics file, and a screenshot of the host with Show details on.

• On the PC: Log tab → Export diagnostics writes one file under %LOCALAPPDATA%\PrismDesk\; Open folder shows it. Report a problem opens a draft GitHub issue with the version, Windows build and GPU filled in.
• On the device: Settings → Report a problem → Share diagnostics, and choose where the file goes. It contains no PIN and no authentication token.

Open the issue from one side only, at Issues, and attach the files. Anything with an order number, a licence key or personal data goes to [email protected] instead.

See also: Known issues · FAQ · Set up over Wi-Fi

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