I appreciate the prompt response, 

The error code DF- DFERH-01 is a Google Play store error that can be fixed by updating or clearing your cache.

1. Open your device's Settings app.
2. Tap Apps & notifications. Then click See all apps.
3. Scroll down and tap Google Play Store.
4. Tap Storage. Clear Cache.
5. Next, tap Clear data.
6. Re-open the Play Store & try your download again.

Once done you can restart your advice. If you still can’t download after you clear the cache & data of the Play Store, restart your device.

1. Press and hold the Power button until the menu pops up.
2. Tap Power off or Restart if that is an option.
3. If needed, press and hold the Power button until your device turns on again.

You can visit this article to find answers to your other QBO mobile questions: QuickBooks Online Mobile app questions.

Feel free to leave a comment below if you have any other questions about QuickBooks Online. I'll be always around to lend a hand.