The Pay for Itinerary UC is called from the Prepare Itinerary UC only if I understood it correctly. This means that it acts on the current just prepared (priced and confirmed) itinerary.
I wonder why the credit card payment flow acts on this itinerary, but choosing to pay with award miles involves selecting an existing itinerary with their price? Isn't it the same current itinerary that we are about to pay?
Also the "Customer not logged in" returns a list of itineraries.
In the alternative flow "Customer Selects Award Travel", one of the steps is "Customer selects award travel", which is unnecessary since we *already found the condition* that the customer selected to pay with Award Travel (that's why we entered this alternate flow). How about this?
Regarding your questions my own interpretation is that the 'Basic Flow' of 'Pay for Itinerary' commences just after the user has selected which itinerary to pay for. In 'Award Travel' they take one step back from this. Yes, it is confusing. They are deliberately trying to be confusing!
I believe that "Customer selects award travel" means they actually click the button to execute this. In other words, the web page will have 2 buttons, one saying 'Pay with Card' and the other saying 'Award Travel'.