The error you're encountering when trying to import the Spine 4.1 package into Unity via the Package Manager URL seems to be related to a network issue or a problem with the Git connection. This type of error often occurs due to network instability or restrictions that interrupt the download process. To resolve this, you can try the following steps:

1. Check Network Connection: Ensure that your internet connection is stable and not being interrupted by firewalls or network restrictions.
2. Try a Different Network: If possible, switch to a different network to see if the issue persists.
3. Use a VPN: Sometimes, using a VPN can help bypass network restrictions that might be causing the issue.
4. Clone the Repository Manually: As an alternative, you can manually clone the repository using a Git client and then import the necessary files into your Unity project.

If these steps do not resolve the issue, it might be worth checking if there are any updates or known issues with the GitHub repository or the Unity version you are using.

@frikic Sorry to hear you were having troubles, glad to hear you've found a solution. Please note that the spine-unity 4.1 runtime does not officially support Unity 6.

I've tried the above package manager URL
https://github.com/EsotericSoftware/spine-runtimes.git?path=spine-unity/Assets/Spine#4.1
with Add package from git URL in Unity 6000.0.37 without any issues. While the error message hints at some other problem (network and firewall related, or perhaps directory write permissions): did you add the spine-csharp package first before adding the spine-unity package? Did that work without issues?

Regarding formatting here on the forum: Please note that you can enclose text or URLs like the ones above in single backticks "`" to format them as inline code, and triple-backticks "```" for multi-line code. Otherwise they are a bit hard to read .