You buy GigSky data plans for your iPad with Apple SIM using the Cellular (Mobile) Data settings on your iPad.
- Tap Settings -> Cellular (Mobile) Data -> Set Up Cellular Data.
- Tap "GigSky" from the list of carriers.
- Tap "View all GigSky data plans", search for your destination, and select it.
- Follow the steps in the GigSky portal.
You can purchase a plan up to 30 days in advance or when you arrive in each country on your itinerary. If you plan on revisiting a country, it might make sense to purchase a plan with a longer time period before expiration, that covers the total duration of your trip.
You cannot buy a data plan for your iPad with Apple SIM using the GigSky app.