This page is for troubleshooting playing Principia levels. When pressing the Play button on a level page it should open Principia and download the specified level, but this relies on your system being properly set up to handle principia:// links. Usually this works without issues, but can have some caveats depending on the platform you are on.
During installation the installer will register the URL handler to where the Principia executable is located. If you have moved the installation files manually without reinstalling then this association will break. Please rerun the installer and install to the new location.
As the portable Windows version does not make any changes to your system, it won't register the URL handler. You can either use the provided play_community_level.bat script to play community levels in a portable manner without modifying the system, or manually add some registry entries to point to where you have the Principia executable. See Windows Portable#Playing community levels for more details.
If you have installed a packaged version of the game or use the AppImage version then the URL handler desktop file should be properly installed to your system. Usually your package manager will update the desktop database for you, otherwise you can try running update-desktop-database as root to update it manually.
Otherwise if you have built Principia from source and haven't installed or packaged it then you will need to set up the URL handler yourself. See Principia Protocol#Linux for more details.
As long as the Principia app for Android is installed, it should be able to handle principia:// links. Have you downloaded it yet?
You can send principia:// URLs directly to the Principia executable which it will parse and act upon. So you can copy the link of a level button and paste it into a terminal to pass as an argument to the Principia executable, like such:
./principia principia://play/lvl/db/11Principia is not a browser game, and it requires the game to be downloaded on a supported platform to work. If you are on an unsupported platform and try to play a level then obviously nothing will happen.
