Fail to purchase at in app purchase with unknown reason

I implemented in app purchase in my app and released. But I failed to purchase product in my app SOMETIMES (not all time).

I have 2 questions.

1. What of case it will happen??

   I test my app, but it haven't occurred. What in case it will happen?? Do you have any similar experiences??

2. How does ": transaction: 180000012369078 - 1" mean?

   This is my device's log at organizer. On success, transaction has number "1" and On failure, transaction has number "2". And formats is not same between on success and failure.

paist my log

On success

Jul 21 12:06:05 unknown adhoc[4714] <Warning>开发者_C百科;: transaction: (null) - 0
Jul 21 12:06:05 unknown adhoc[4714] <Warning>: purchasing
Jul 21 12:06:18 unknown adhoc[4714] <Warning>: transaction: 180000012369078 - 1
Jul 21 12:06:18 unknown adhoc[4714] <Warning>: purchased

On failure

Jul 20 19:50:41 unknown adhoc[2202] <Warning>: transaction: (null) - 0
Jul 20 19:50:41 unknown adhoc[2202] <Warning>: purchasing
Jul 20 19:50:41 unknown itunesstored[2273] <Notice>: MS:Notice: Installing: com.apple.itunesstored [itunesstored] (550.58)
Jul 20 19:50:41 unknown itunesstored[2273] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Activator.dylib
Jul 20 19:50:44 unknown itdbprepserver[2270] <Warning>: Running Create Triggers...
Jul 20 19:50:46 unknown adhoc[2202] <Warning>: transaction: 70AAEAAE-22DF-4927-A6FA-4ECF4783619D - 2
Jul 20 19:50:46 unknown adhoc[2202] <Warning>: failed
Jul 20 19:50:46 unknown adhoc[2202] <Warning>: unkwown

Please help. thank you.

Once the purchase has failed, print the error description using [transaction.error localisedDescription];.

It may fail because the wifi connection is weak, and it bails out with the description Error : Cannot Connect to iTunes Store.

Reset all settings in your device if this is the error. I solved it like that!