Update from 4.0 to 4.2.9 beta at early time and get this error, fix it by import binary file instead of json file.
But when upate to new spine-unity unitypackage(2024-03-06), encounter the same error.
Error reading skeleton JSON file
During the beta there is no guarantee that runtimes can read beta editor exports. The beta changed the binary format last night to add a physics limit feature. We'll update spine-unity likely today. Until then you can use 4.2.27-beta, which the 4.2-beta spine-unity can read.
Or you can use JSON exports for beta editor versions, as JSON is less sensitive to export format changes.
@JustHitIt Sorry for the troubles! We've just pushed a commit and published a new 4.2-beta spine-unity unitypackage, available for download here as usual:
https://esotericsoftware.com/spine-unity-download