I did it with this tutorial: Unreal Engine 4 - Mixamo to Unreal Engine 4 - FBX Import - YouTube
The only difference is that I used an other character instead of my main character. Could it be possible that I have to retarget (atleast human characters) the model with the SK_Mannequin like he did in the Video? I did everything until 8:50 but I just replaced my Enemy-Actor Mesh with the mesh from Mixamo. I cant try it until tomorrow.