If you refer to the spigot page, you'll see that the plugin doesn't currently support 1.21.1. Also you're not even running the newest version of InvSee++? The current release is v0.29.3. If you update ...
bug in other softwareThe issue is caused by the server software, other plugins or BuildToolsThe issue is caused by the server software, other plugins or BuildTools I can turn off that option, but as ...