If you have purchased Just Press Record on one iOS device - say your iPhone - and then try to download it on your iPad, the App Store may ask you to purchase the app again rather than show your the Download button. This appears to be an issue with the new App Store introduced with iOS 11.
Once purchased, you can download the app again for free on any device that is signed in to the same App Store account (or Family Sharing group).
If you are being asked to pay again, rather than downloading the app from the App Store product page, locate it in your purchase history.
You can see your purchase history from inside the App Store. Tap the avatar in the top right corner to see your App Store Account details. There is a ‘Purchased’ section from where you can see and download any app you have purchased in the past.
Please note that the Mac version is a separate purchase on the Mac App Store.