Animation retargeting

Hope someone can help,

I have followed several tutorials on retargeting character animations and it seems I am faced with character either vanishing warping even after many hours of step by step guides like for like guides on version 4.27 using characters intended for this. Only character assets that appear to work are Paragon ones? Is there a speedy solution I would like to be able to purchase and use new models and get them rigged with ease.