"The package must contain at least one organization and one item in order to be added to Learning Store."

Thanks for the update and the additional information, Steven.

With your permission, I'd like to take a look at your project file to investigate what's happening and upload it in another LMS environment to see if it's successful. This will help us determine if the issue lies within the project file or the LMS.

You can share it publicly here, or send it to me privately by uploading it here. I'll delete it when I'm done troubleshooting.