Object is transparent in Unreal Engine

Hi guys!

I’m trying to learn Blender and Unreal Engine as I want to challenge myself to make a small game. I created a pretty simple medieval window, and exported as a .fbx and imported to Unreal Engine 4.26. However when I add it to the scene, the backside of the object is transparent.

I’m adding some pictures for you to see, hopefully someone understands what I have done wrong!

I have flipped the normals, but I don’t know if I did it correctly…

For me ii looks like your normals point to the inside and Unreal shows excactly thats… the inner polygons… so you said you flipped them… why?

I thought that was what I was supposed to do. Also, I’ve tried flipping them back, and I had the same problem except now it was on the backside

You have a a one sided material and it is supposed to be something likes this.
If your normal points to the outside like so:

1==>     <- |         <==2

Your object is visible from view (1) and also a little more from above and below. If you look from (2) then iit is nor visible… if you look more from above you can ssee the inner part of the lower polygons and looking from below the upper polygons. If you wanna see you object also from behind you have to add polygons to close the open areas.