title: Why MKStoreKit isSubscriptionActive method is always returning NO?
body: <p>Working in an app that uses StoreKit through MKStoreKit, I have noticed that the method for checking if a subscription is still valid is always returning 0 (NO or false). </p>
  
  <p>I've tracked the error and I found that inside the method <code>- (BOOL) isSubscriptionActive:(NSString*) featureId</code> the <code>jsonObject</code> generated by this line:</p>
  
  <pre><code>id jsonObject = [NSJSONSerialization JSONObjectWithData:subscriptionProduct.receipt options:NSJSONReadingAllowFragments error:nil];
  </code></pre>
  
  <p>is <code>nil</code>.</p>
  
  <p>Then I checked the error returned from this method, which is:</p>
  
  <blockquote>
    <p>[MKStoreManager isSubscriptionActive:]] Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (No value for key in object around character 15.) UserInfo=0x200c0300 {NSDebugDescription=No value for key in object around character 15.}
    (lldb) </p>
  </blockquote>
  
  <p>So then I checked the receipt and I found that the problem is that the supposed "JSON Receipt" is not a JSON, since it uses "<code>=</code>" instead of "<code>:</code>". I suppose that someone has already been dealing with this issue, so what is your solution?</p>
  
  <p><strong>EDIT</strong>
  I'm working with sandbox environment.</p>