Unable to download an app in iOS 12

I am unable to download an app that I wish to use on an iPhone running iOS 12. Tapping the download button shows the download progress indicator, but the app download doesn't start.

The app store page of the app shows the following message:

The developer of this app needs to update it to work with iOS 11.

I am not using iOS 11, but iOS 12, running on an iPhone 8. So shouldn't the app download fine?

What can I do to install this app?

There is no way to download and install this app (unless the developer of the app updates it to work).

The developer of this app needs to update it to work with iOS 11.

The above message is a bit misleading and is applicable for devices running iOS 11 and later.

The app in question is built in 32-bit mode only. An iOS app could be programmed by the developer in either 32-bit mode, 64-bit mode or both. (Note that only one single app is hosted on the App Store, no separate 32-bit and 64-bit version).

Apple started supporting 64-bit apps first with iPhone 5s which featured a 64-bit processor. All the subsequently released models of iPhone feature 64-bit processor.

Apple has stopped supporting 32-bit only apps starting with iOS 11. To run such apps on iOS 11 and later, the developer need to re-program it with support for 64-bit mode.

If you wish to use the app, your only resort would be to find an iOS device running iOS 10 or earlier (which supports the app), or contact the developer of the app and request them to update it with 64-bit support. You can find the contact information for the app developer on the App Store page of the app.

This is the official explanation by Apple as mentioned on the Apple Support page, About iOS 11 Updates:

iOS 11 is performance optimized for 64-bit apps. 32-bit apps will need to be updated by the app developer to work with this version of iOS.

Again, the same is applicable for iOS 11 and later.