How do I install Spine for 2D Character assets?

Use the Spine-Unity runtime version that matches both the Spine export version used by the asset and your Unity version. Download it from the official Spine-Unity page, then follow the version and import instructions in the asset's included guide.

Do not install an arbitrary older runtime package, because a runtime and exported-data version mismatch can cause import or animation errors. If an error remains, send the asset name, Unity version, Spine runtime version, and the complete first Console error to support.