Due to an agreement between Kobo and Apple, the Kobo App for iOS doesn’t include the Kobo store.
If you use an iOS smartphone or tablet, you’ll need to buy your eBook or audiobook on kobo.com. Once your transaction is complete, your audiobook will then appear in your Kobo App for iOS.
You can always add a shortcut to your iPhone or iPad so that you have easy access to the Kobo Store. Read the article below to learn how: