I don't understand why you can't just attach a child order to any order in TWS. Currently you can only attach some auto stop or bracket order to an existing order. After you have done that, the "key field" indicates that the orders are related. I would expect that, when inserting a random order in TWS, one could use this key field as a parameter to couple that order to any other (existing) order. But obviously that's not possible. Any ideas on how to solve this? Or why it's not possible?