I made a GetItemTransactions call and TransactionArray is not present. Under what conditions is TransactionArray returned?
The GetItemTransactions call, by default, returns transactions from up to 30 days ago (from the time that the call is being made). What this means is that if a transaction ended 31 or more days ago, the GetItemTransactions response will not contain TransactionArray.
To remedy this, you need to include ModTimeFrom and ModTimeTo, and specify the date range in which that transaction took place. The request will look something like this:
This request will return items between 7-30-2008 and 8-07-2008. Without these dates, the call would have returned transactions taking place between 9/16/2008 and 7/16/2008 (the date as of this article being written is 9/16/2008).