Cannot Export Blender Animation in a right way

Hi guys have a question. I want to export a box model from Blender to Unreal. Only the cover should be animated. I have adjusted the units to 0.01 from the rig and mesh. I have animated only the cover with a bone. The problem is when I export FBX I get an error message from Unreal and in Unreal the box animates but not the cover opens but the whole mesh. Can you help me what the problem is.