Spine is the editor (the program in which you make skeletons and animations),
the runtime is the code you have to add into unity/other game engine to make it work, together with your spine exported files (the ones with your characters/animations/images). you can find the runtimes here: Spine: Runtimes
As Pharan wrote to you:
Pharan लिखाThis version of the runtime looks a bit old.
You probably downloaded the runtime some time ago, but it god updated. You need to download the new runtime and replace the one you already have in unity with the new one.