I am making a product package and when i am adding the top flap as well as the below flap which closes the box in map art in extrude and bevel it doesn't appear. Can you guide me please.
You should be able to do what you are trying without much issue.
I'm not 100% clear what you mean by "adding the top flap as well as the below flap which closes the box"
I'm imagining something like a cereal box with 2 flap top... you can't do that in Illustrator's 3D. Each panel can only use one symbol. If you are trying to add two symbols to a single panel, you can't. So, set up the symbol art to appear how you want that panel to appear as a single symbol.
Merely set up the base art and covert the sides/panels to symbols. Note, you extrude a rectangle for the overall shape, I didn't bother with a symbol for the front face, but if there's art there, that'll need to be a symbol as well.
From there, choose the
Effect > 3D > Extrude & Bevel then the
Map Art button.
Note that in the Map Art dialog window there are two colors of sides. Some sides will be a dark grey, and some will be a light grey. The dark grey indicates a currently hidden side. Light grey indicates a visible side in the current set up.
You'll want to apply your symbols to the light grey panels.
That should give you the proper set up:
This is quick and dirty.. but here you can see a single symbol indicates a 2 flap top panel:
(CS6 screenshots, but it's essentially the same in newer versions. Adobe hasn't touched the 3D effect in years.)
Anything more complex box than an extruded simplest possible rectangle can have much more surfaces than 6. For example only have a stroke in the rectangle, you have straight away 16 surfaces, 10 of them invisible. Have some foldings, then you have much more.
You must find which are the visible. Remove the unnecessary strokes. Test also with some simple symbols to see if your art symbol has something not able to be shown correctly.