You can create nested categories by using category groups. You can do so from the categories tab, that you can open by tapping on the corresponding icon in the bottom bar.
Adding a new group
Tap on the + button on the bottom-right of the screen
Select Add group
Fill the details
Tap Save
Assigning a group to a category
Open the create/edit category screen (check the question above)
From the Group dropdown menu select the group you want this category to belong to
Tap Save
You can do so from the categories tab, that you can open by tapping on the corresponding icon in the bottom bar.
Creating a new category
Tap on the + button on the bottom-right of the screen
Select Add category
Fill the details
Tap on Save
Modifying an existing category
Long press on the category you wish to modify
Tap on Edit
Change the details you want to modify
Tap on Save
Deleting an existing category
Long press on the category you wish to modify
Tap on Delete
Tap on Ok in the confirmation popup
Open the Tools screen by tapping on the corresponding tab icon in the bottom bar
Tap on Settings
Tap on Currencies
Select your preferred currency
Tap on Ok in the confirmation popup
Make sure the Google Play Store app installed on your device is up to date
Open the Play Store app
Open the left sidebar by clicking on the hamburger menu in the top left
Tap on Settings
Scroll down and tap on Play Store version (one or multiple times)
If the app is up to date you will see a popup telling you so, otherwise the update process will start
There are two different ways to backup your data: automatic system backup, and in-app backup
Automatic system backup
Android supports automatical backup of your data, including Whole's app data. To know how to set it up please visit this page on Android's official Help Center.
In-app backup
The in-app backup lets you perform snapshots of your data at any point in time and stores them in your cloud storage (Google Drive or Dropbox).
Note: this feature is available for premium users only.
Backup your data
Open the Tools screen by tapping on the corresponding tab icon in the bottom bar
Tap on Backup
If you're not signed in: sign in with your service of choice
Select the folder you want to store the backup in
Tap on the Backup button
Optionally select an auto-backup frequency if you want to have Whole periodically backup your data
Restore a backup
Open the Tools screen by tapping on the corresponding tab icon in the bottom bar
Tap on Backup
Tap on the Restore button
Select the backup file
Tap on Ok in the confirmation popup