To store images and files for your Custom Fields the app requires that an additional "assets storage" theme be created in your store. This theme is not visible to customers visiting the site, it is simply a placeholder for storing images and files.
The app will attempt to create this theme automatically called:
DO NOT DELETE - Custom Fields Assets Storage
This is what the theme will look like in your store's admin:
The most important thing to note is that you MUST NOT DELETE THE THEME. If the assets storage theme gets deleted then any images/files uploaded to that theme through Custom Fields will be deleted permanently.
I Get a Message About Needing to Delete Another Theme
Shopify has a max limit of 20 themes per store. If your store has 20 themes you will need to delete one of the themes in order to use Custom Fields image and file fields.
If you are unable to delete a single theme from your Shopify store, you can upload images and files to your own Amazon S3 bucket by using the Plus plan. More info about setting up your own Amazon S3 bucket can be found here.
Can I Backup My Custom Fields Files
Yes! At anytime you can visit Online Store > Themes in the admin section of your store and download the theme file. Next to the Custom Fields Assets Storage theme click "Actions" and then "Download theme file".
The theme and all images/files in it will be zipped by Shopify and a download link will be emailed to you.