It seems this is a network issue from Unity. There is an explanation from Unity’s user manual as following:
“In some corporations and institutions, users are behind a firewall and can only access the internet through a proxy. Some proxies unpack the HTTPS content and repack it with its own self-signed certificate. Unity Package Manager’s underlying HTTPS layer rejects these self-signed certificates because it does not recognize them, and treats the connection as a possible man-in-the-middle attack. This means that you can’t use the Package Manager in Unity if your proxy uses a self-signed certificate.”
Our Unity XR platform SDK has some dependences with Unity’s official packages, therefore, this may be the root cause of this issue. These resources may provide some help:
Unity - Manual: Network issues (unity3d.com)
Network configuration - Unity Forum