Invisible faces

Hello eveybody,Recently i was trying to Model a 3D Fence to finish my house design.
Here’s the Design on the Object mode-Solid:

So when i attempted to texture it i found that there’s some messing faces on the model but it was in the Solid mode,Some fellas told me to go to Mesh-faces-Flip normals and some told me to try Mesh-faces-beautify fill,But Flip normals fixes the big ones as the picture will explain to you:

And beautify fill just handles only the big ones:
I hope you help me i’d be grateful :slight_smile: