Skeletal Nanite Assembly help please!

I’m working on exporting trees that I am creating in Blender, over into Unreal as Nanite Skeletal Assemblies.

The trunk is a basic mesh, that I have rigged.

The leaves were placed via instancing in Geometry Nodes.

My goal is to make a library of trees, that use the same leaf/small branch instances, so I am using unreal:naniteAssembly:meshAssetPathto reference components I’ve already imported into Unreal.

I’ve managed to export this from Blender into UE5.7 as a static mesh assembly - I have that pipeline working great - no problems there.

The next stage in my quest is to get skeletal mesh assemblies working. This is proving considerably harder.

I was wondering if someone could look through my USDA file and point me in the direction of where I am going wrong?

I get this error when importing into UE:

[E:/personal/doug_fir/USD_04/rigged/export/MySkeletalAssembly_skeletal_assembly.usda : ‘’, Unknown] There was no data to import in the provided source data.

I feel like I am close, but have no idea where I am going wrong on this one.

MySkeletalAssembly_skeletal_assembly.usda (10.6 KB)

I should mention the component parts are skeletal meshes -