Blender -> UE4 : don't export skinning

Hi guys !

As Unity Developper, I’m begginer on UE4, i never this issues on Unity.
I think it’s just about a FBX import settings.

I’ve design a hidden stair, rigged with a only 1 bone,
I put a progressive weight painting on each stair.

This weight painting works fine on Blender. But once exported on UE4, the skinning look be at 1 on each vertex.

Blender Preview UE4 Preview
Test23.jpg

Test27.jpg​​​

Could you help to solve this problem ? or indicate me a simillar topic (Don’t find by myself :D)