Why my 3d model surface are not getting exported properly

[kumari_priyanka]

[Chuk_Chuk]

Maybe it is flipped normals?

Select all faces of your mesh in edit mode and then press shift+n, to recalculate the normals

[kumari_priyanka]

I have checked the normals are correctly oriented

[kumari_priyanka]

i have correctly oriented my normals still when i export my model its few surfaces are not visible.