That's a new one to me but I never use an iPad to buy stuff; I dislike the app. I'm not even certain the reason I don't like it just that it seems weird to navigate.
Can you migrate to a desktop and take a look at what you see there in your Purchase History? Very, very few sellers designate listing something for Local Pickup Only because it seriously hampers the number of people who might want it.
If not, try to Contact your Seller for clarification. If it's a glitch, I'm certain they can send you a new invoice with proper postage to pay.
Best of luck. Let us know what you learn if you have time to think about doing that.
