CreateJoint- no bodies defined at body and body1, joint prim?

Hi, I put the robotic arm into the robot asset and click on play. The following question will appear. How should I set it up?

this is most likely because you nested rigid bodies, so the nested rigid bodies were not create. Nesting rigid bodies is not allowed because in USD there is a local transformation stack, so we really dont know the order.

To simulate something like this, what you can do is to put both robots on the same level in the USD hierarchy and connect them with a fixed joint.
You can either exclude the joint from the articulation (there is a bool on the joint) - this way two articulations will be created that are connected through a maximum coordinate joint. Or you dont exclude it, in which case one articulation is created for the whole topology.