title: Fail to purchase at in app purchase with unknown reason
body: <p>I implemented in app purchase in my app and released.
  But I failed to purchase product in my app SOMETIMES (not all time).</p>
  <p>I have 2 questions.</p>
  <ol>
  <li><p>What of case it will happen??</p>
  <p>I test my app, but it haven't occurred.
  What in case it will happen?? Do you have any similar experiences??</p>
  </li>
  <li><p>How does &quot;: transaction: 180000012369078 - 1&quot; mean?</p>
  <p>This is my device's log at organizer.
  On success, transaction has number &quot;1&quot; and
  On failure, transaction has number &quot;2&quot;.
  And formats is not same between on success and failure.</p>
  </li>
  </ol>
  <p>paist my log</p>
  <p><em>On success</em></p>
  <pre><code>Jul 21 12:06:05 unknown adhoc[4714] &lt;Warning&gt;: transaction: (null) - 0
  Jul 21 12:06:05 unknown adhoc[4714] &lt;Warning&gt;: purchasing
  Jul 21 12:06:18 unknown adhoc[4714] &lt;Warning&gt;: transaction: 180000012369078 - 1
  Jul 21 12:06:18 unknown adhoc[4714] &lt;Warning&gt;: purchased
  </code></pre>
  <p><em>On failure</em></p>
  <pre><code>Jul 20 19:50:41 unknown adhoc[2202] &lt;Warning&gt;: transaction: (null) - 0
  Jul 20 19:50:41 unknown adhoc[2202] &lt;Warning&gt;: purchasing
  Jul 20 19:50:41 unknown itunesstored[2273] &lt;Notice&gt;: MS:Notice: Installing: com.apple.itunesstored [itunesstored] (550.58)
  Jul 20 19:50:41 unknown itunesstored[2273] &lt;Notice&gt;: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Activator.dylib
  Jul 20 19:50:44 unknown itdbprepserver[2270] &lt;Warning&gt;: Running Create Triggers...
  Jul 20 19:50:46 unknown adhoc[2202] &lt;Warning&gt;: transaction: 70AAEAAE-22DF-4927-A6FA-4ECF4783619D - 2
  Jul 20 19:50:46 unknown adhoc[2202] &lt;Warning&gt;: failed
  Jul 20 19:50:46 unknown adhoc[2202] &lt;Warning&gt;: unkwown
  </code></pre>
  <p>Please help. thank you.</p>