Can I use the app on both iPad and iPhone?

You certainly can have the app on both your iPad and iPhone, here's how:

• Make sure the device you want to download the app onto is logged into the Apple ID used to buy the app originally.
• Tap the App Store app.
• Tap Updates.
• On iOS 11 and up, tap your photo in the top right corner. On earlier versions, skip this step.
• Tap Purchased.
• Tap Not on This iPhone to see all apps you've bought that aren't installed here. You can also swipe down from the top of the screen to reveal the search bar.
• When you've found the app you want to install, tap the iCloud icon (the cloud with the down-arrow in it) to download and install it.