You own the assets you create with Spine: project files, JSON and binary data, video, images, and texture atlases. You can sell those or give them away free or do whatever you want with them. If someone wants to use the Spine Runtimes, they need a Spine license. So if you have scripts or other software which contains the Spine Runtimes, others won't be able to distribute that without a Spine license. If you sell JSON/binary data, you probably want to let your buyers know they'll need a Spine license to be granted permission to use the Spine Runtimes. Of course the Spine license also lets them use Spine to edit the projects, which will be helpful.