What are prerequisites for auto posing the target character?

A successful pre-process (Setup bone names) on the target character must be run before this step.

You need to have UE4 mannequin in the scene and correctly selected in the Uefy Script Panel options. The type must be set to Epic Skeleton or Custom Mapping depending on the bone hierarchy of the target character.

If your target character does not have an Epic Skeleton then custom mapping and custom roll values in the script must be set correctly. An example mapping for Fuse CC character rigged with mixamo service is provided in the script by default.