Contact
If a forecast was wrong
The figures come from a weather service and the app draws them as they arrive, so a day that turned out sunnier than predicted isn’t something I can fix. What I can fix is the app getting in the way of them: no cities where there are plainly some, a temperature on the map that disagrees with the city you tapped, a filter that keeps something it should have dropped. Those are worth writing about.
What helps
Your device and iOS version, roughly where the map was, which day the slider was on, and any filter you had set. A screenshot says most of that at once.
Plus, and refunds
Apple takes the payment and Apple handles refunds, so there is nothing on my end that can charge you or pay you back. Cancelling is done in Settings › Apple Account › Subscriptions. If a subscription you’ve paid for isn’t being recognised, though, that’s mine to sort out — tell me and try Restore Purchases in the app’s settings in the meantime.