Problem with creating Apex cloth rig in 3dsMax


Yesterday I was following this video to create apex cloth:

I can create the apex Cloth modifier with my mesh and paint it without problem.

But when I try to create a rig for my cloth mesh, It gave a warning saying: “Error: unknown Rig. Can not find its root bone”

I can still export my cloth to ue4 and make it work in game, but without creating rig, I can’t make it collide with bones.

Anyone else encounter this issue before?