Parrot tech support reached out to me and advised me it is impossible to do the In-App Purchase of Flight Plan on IOS before the 15 day free trial of Flight Plan is over. The purchase will be blocked until after the 15 day trial is up. Then the user will be prompted to do the In App Purchase of Flight Plan, but if you try to purchase before the 15 day trial is up the purchase just won't go through the iTunes App Store.
I hope they make it a bit clearer so people don't try to buy prematurely and get blocked.
I might have figured this out. In IOS Flight Plan does not activate until you actually connect a drone. I wanted to get started using it and making maps, but it seems like the drone must be present for it to activate the in app purchase from the iPhone.