HELP, The normals of my model flip when exporting.

Hi, first of all sorry for ask for help as a first post

Here you can see my model in unity

The one on the left has the normal pointing towards the outside in blender, the one on the right has them towards the inside, they are both on the exact same position.

As you can see neither one works properly, the one on the right gets the light from the wrong direction and look diffuse even though it has a specular matt, the one on the left its just terrible wrong.

This is the one on the right on blender:

and this is the one on the left:

I’m sure its just a silly mistake from my part, any help will be greatly apreciated.

Cheers

any ideas?

Maybe check for non-manifold geometry in your mesh before exporting?
While in Edit Mode:
Mac: Ctrl Opt Shift M
Windows: Ctrl Alt Shift M

Also removing duplicates and recalculating normals would be a good idea.