Blender Materials are not per default compatible/ interchangeable with Unreal Materials. If your Blender Material is more complex than:
[Image] → [Material]
You typically need to rebuild the Material in Unreal Engine.
Another way would be Baking your Blender Material into one Texture. Like this
This process might be a bit difficult the first time around, but once you get the hang of it, it´s very useful.
Bonus Tip: I can HIGHLY recommend the Bake Tool Add On for Blender. It has saved me so much time and frustration.