Let me chime into this thread, info2016. I'm here to help you clear the cache on your phone for the QuickBooks App.

Clear cache means getting your app clean. This will help you see if your customer has viewed their invoice. Allow me to provide the steps on how to do it.

For Android users, here's how:

1. On your phone, go to Settings.
2. Select the QuickBooks Online application.
3. Click the Refresh Data, and then choose Yes.

For iOS users, these are the steps:

1. On your phone, go to Settings.
2. Click on General, and then choose iPhone Storage.
3. To free up the storage without deleting the documents and data for the app, select Offload App.

You can also consider uninstalling and then reinstalling the mobile app. Ensure it's running the latest update to prevent changes from your experience when using it.

Keep in touch if you have other questions regarding your invoices. I'll be around to assist further. Have a great rest of the day!