Animation Retargeting does not work ('crumples' my mesh)

Hi! I am new to animation retargetting and after I made my character to blender, imported it to Unreal and retargetted the skeletons, the animation from UE’s mannequin seems to be not working. My character (image above) is what appears when I retarget the animation from the mannequin while the image below is what it should look like. I have tried many methods already like re-skinning, reimporting and fixing to the accurate pose but none seemed to work.
Every help is much appreciated, thank you!