If you want to download your invoices, you can do it by following these steps
Tap on your picture next to the notifications bell - top right corner
Tap on the settings wheel - right, top corner
In the Profile and Settings menu, tap "Bills & Purchases," then open the Purchases list
Press the blue button "See transactions"
Each invoice has a download button that you can use to download them to your phone If the invoice has already been downloaded to your phone, it might not work to download it again. Look for the invoice in the Downloads menu on your phone