You've come to the right place for assistance with all things QuickBooks, @Cheshire. I'm here to provide some info regarding the no invoice icon on your QuickBooks App.
To help you resolve these issues, I have some helpful tips.
Fix other app-related issues.
Here are some quick steps to fix most app-related issues:
Change the Wi-Fi data connection on your device to 4G (varies by device).
Close and restart the app.
Clear app data. To do this:
Open your device Settings.
Select apps (varies by device).
Choose the QuickBooks app from the list, then select Storage.
Select clear data.
Power down and restart your device.
Uninstall and reinstall the app.
If the issue persists, I recommend uninstalling and reinstalling the app. Alternatively, you can use the mobile browser to generate invoices.
I'm also adding these helpful modules you can browse about personalizing invoices and setting up estimates in QuickBooks Online: