FBXImport Error, Unable to triangulate mesh. Can't import fbx, what could be and how to fix it?

[David_Mustaqim]

So, i get the same problem and this my conclusion.

So somehow Unreal Cannot triagulate the unique topology (see the picture)

So, what i did, is i seperate the unique topology, and then add Triangulate modifier, and then apply it.

After that, go to face > Tris to Quads or simply press Alt + J delete diagonal edge.

And after that you can export it to Unreal.