It is possible for a Developer to upload a build directly from within the Luna Playable plugin in Unity:
Make sure all game changes have been made (size optimisation, Playground fields etc.)
Open the Luna Playable plugin window from within Unity (Ctrl+E) and ensure you are signed into the correct account
Navigate to the "Playground" tab
Click "Build & upload"
Wait for the progress bar to complete in the bottom left of the window, after it does your playable will appear in Playground
Alternatively a Developer can manually upload a Playground build by following these steps:
Open the Luna Playable plugin window from within Unity (Ctrl+E)
Select the arrow on the right of the build button and select "Build Playground"
Press the build button after selecting this and wait for the progress bar to complete
In your project directory locate your "LunaTemp" folder, and from within there the "stage4" subfolder. In there will be a
Navigate to Luna Playground in your browser and ensure you're signed in.
Drag and drop the
playground.zipfile to the cloud icon in the apps page in Playground.
(You can also drop the file over an existing build's cloud icon to update it)
You can read about this process in greater detail here.