Both Apple Pay and Curve send instant notifications, which means you’ll be notified twice every time you pay with your Curve card on Apple Pay (potentially three times if your underlying payment card also gives you instant notifications).
If you don’t want to get two notifications for every transaction, you can turn off notifications in Apple Pay for your Curve card.
To do this, go into the Wallet app and tap on your Curve card. Then, tap the icon in the top right corner. Scroll to the Transactions section and tap the “Allow Notifications” toggle to turn off.