Retargeting Animations onto a MetaHuman

The problem about Retargeting Animations onto a MetaHuman. I do all the things according to the docs. But when it comes to Step 3 selecting skeleton from Duplicate Anim asset and retarget>, there is no even any skeleton in the list. Reopen UE or the PC. Still no improvement.

I’d really appreciate if anybody know where the problem is… This really drives me crazy