Gonna attempt to add this to an avi. Idk how to work blender

Mikiloolu, Have u weight-painted it to the avatar? or something you've done to the avatar in blender has broken it for example

1. Weightpainted it to the wrong bone/ attached itself wrong
2. in unity you might want to reimport or delete an redo the avatar

Add this to my avatar and put it in playmode it breaks my left and right arm.I delete the Sweater completely and it stays broken my arms wont move anymore.Help