Problem Downloading Google Duo

Hello,

Try following these steps:

Connect to Wi-Fi

If you’re using cellular data or Wi-Fi and have issues with an app, try to connect to another Wi-Fi network. Learn how to connect to Wi-Fi on your iOS or iPadOS device, on your Mac, or on your Apple Watch.

To check your Wi-Fi connection, try streaming a video from the Internet to see if it loads quickly. Or contact your Internet provider for more help.

Pause and restart the app download

When you firmly press the app from the Home screen, you might see options to Resume Download, Pause Download, or Cancel Download. If the app download is paused, tap Resume Download. If it's stuck, tap Pause Download, then firmly press the app again and tap Resume Download.

Restart your device

If the app appears on your Home screen but is dim or has a white grid with gray lines on it, don't delete the app. Restart your device, then go to the App Store and redownload the app. Learn how to restart your iOS or iPadOS device, Apple Watch, or Apple TV. 

If you delete an app, you might lose the content associated with it.

Get more help

If you still have issues with apps on your device, contact Apple Support.

Thanks, EpicX

In that case, I would contact Apple Support here:

https://getsupport.apple.com

Have a good day :)