The plugin cannot be installed online
Download the case project and report an error
Hi @coke2025, welcome to the community!
Our packages are hosted on github.com, so your system will need to be able to contact that server. Specifically, for the latest release, you’ll need to be able to download from here:
https://github.com/CesiumGS/cesium-unity/releases/download/v1.15.2/com.cesium.unity-1.15.2.tgz
Can you check if that is working on your system / network?