Is In-App purchase applicable for eBooks/Audiobooks?
<p>We are a book store selling hard covers, ebooks and audiobooks. 
We have a website where we accept credit cards for online payment from customers. 
We also have an iOS and Android app where user can read/listen the purchased books.</p>

<p>Now we want to sell the ebooks and audiobooks via our iOS native application (and Android app as well in future). 
Customers will be able to buy ebooks/audio books from our app and can download and read them in all the platforms. 
We have a pretty large number of book titles, 50K+ and its extending. </p>

<ul>
<li><p>What would be the best way to implement this?</p></li>
<li><p>Is in-app purchase mandatory for this? Or should we use the existing credit card payment system?</p></li>
</ul>