For information of retargeting animation, see Animation retargeting and Retarget animation from one skeleton to another.
Error: Skipping arm retargeting since arms are not labelled
Some of the joints in your arm joint chains are not labelled. All joints, including all those in the hands, must be labeled for a successful retarget.
See Label a skeleton’s joints and Skeleton > Joint Labelling > Add Retargeting Labels.
Error: Skipping legs and arms since labels are not found
Some of the joints in your arm and leg joint chains are not labelled. All joints, including all those in the hands and feet, must be labeled for a successful retarget.
Each arm and leg joint chain must have joints labelled as a a Shoulder, Elbow, and Hand or a Hip, Knee, and Foot.
One of the joint hierarchies (source or target) that you selected for the retarget has a different number of limbs than the other. The retarget solver can not solve between skeletons with different numbers of limbs (for example, single-headed source skeleton > two-headed target skeleton).