When I GetRepackedSkin,i had a error.
Graphics.CopyTexture could not find destination D3D11 texture object. Maybe it is a RenderTexture that is not created yet?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Spine.Unity;
using Spine.Unity.AttachmentTools;

public class TestSpine : MonoBehaviour
{
    public SkeletonAnimation blackbear;
    public SkeletonAnimation greenbear;

private Material _runtimeMaterial;
private Texture2D _runtimeAtlas;
void Start()
{
    StartCoroutine(ChangeSkin());
}

IEnumerator ChangeSkin()
{
    yield return new WaitForEndOfFrame();
    greenbear.gameObject.SetActive(false);
    yield return new WaitForSeconds(3f);

    Spine.Skin SkinDefault = blackbear.skeleton.Data.FindSkin("_Default");
    Spine.Skin Skinhead = greenbear.skeleton.Data.FindSkin("hat");
    Spine.Skin skinMix = new Spine.Skin("Mix");
    skinMix.CopySkin(SkinDefault);
    skinMix.AddSkin(Skinhead);

    blackbear.skeleton.SetSkin(skinMix);
    blackbear.skeleton.UpdateCache();
    blackbear.skeleton.SetSlotsToSetupPose();

    if (null != _runtimeMaterial)
    {
        Destroy(_runtimeMaterial);
    }

    if (null != _runtimeAtlas)
    {
        Destroy(_runtimeAtlas);
    }

    Spine.Skin repackedSkin = skinMix.GetRepackedSkin(
    "RepackedSkin",
    blackbear.skeletonDataAsset.atlasAssets[0].PrimaryMaterial,
    out _runtimeMaterial,
    out _runtimeAtlas
    );

    skinMix.Clear();

    blackbear.skeleton.SetSkin(repackedSkin);
    blackbear.skeleton.UpdateCache();
    blackbear.skeleton.SetSlotsToSetupPose();

    Destroy(greenbear.gameObject);
}
}

I have finished processing, set the mesh type to FullRect.