Tried all the tutorials I could find but they all either go in the other direction or are just for animations.
After the 'retarget to another skeleton" I get the error
“The Preview mesh hierarchy doesn’t match with Skeleton anymore. Would you like to regenerate skeleton?”
If you say yes, the next time you open that skeleton or new mesh you get it again.
The best way to get your Mixamo character working is downloading it as UE4 skeleton. If you are using the Mixamo’s default skeleton mesh and you want target their skeleton to the UE4 skeleton, you can use the Retarget Manager in the Unreal Editor.