I have already created an Apple coupon discountcoupon.pkpass. I uploaded it on my public server and I gave direct download link. When I open that link in my iPhone or iPad, iOS doesn't recognize the pass.
How can I give download link on my website? When the user click in my coupon link, it should show the Wallet add pass screen.
You need to set the MIME type to application/vnd.apple.pkpass for iOS to recognise the file as a pass and to open Wallet.
See this question for how to do that.