title: iOS: In-App-Purchase fails for some users in production
body: <p>I've recently released an iPad app which has a non-consumable "pro upgrade"-style In-App-Purchase.</p>
  
  <p>It works for most users, and it worked when testing. However, I do get daily reports of the IAP crapping out for some customers of the app.</p>
  
  <p>It is the worst kind of bug:</p>
  
  <ul>
  <li>For most people, it seems to work fine. </li>
  <li>For some people, it works after a reboot of the device or logging out from the App Store. </li>
  <li>For
  some other people, nothing seems to help and they can't make the
  purchase.</li>
  </ul>
  
  <p>And I do not have any remote logging implemented...</p>
  
  <p>This seems to happen across various locales / different iPad models / OS versions.</p>
  
  <p>For those which can't make the purchase, usually an error pops up which says that their Apple ID password is incorrect, after confirming the purchase.</p>
  
  <p>The purchase button in the app only appears after the IAP product was received from Apple's server successfully.</p>
  
  <p>I am not sure how to track down what's going on there. I was initially thinking it's on Apple's side, but the number of people reporting it tells me it must be something with my app.</p>
  
  <p>Any best practices on how to debug this?
  thanks!</p>