Recently migrated a site that's using Metabox. Purchased license so fully registered.
In need of modifying a field, but do not see anything listed under 'Custom Fields'. Does this need to be imported in? All the fields/listings show correctly on the site, but in need of making a small change and likely future changes.
It is possible that the meta boxes and custom fields are created by coding instead of the Builder (Meta Box > Custom Fields). Please follow this documentation to get more info https://docs.metabox.io/creating-meta-boxes/
You can try to deactivate all plugins except Meta Box and switch to the standard theme of WordPress (Twenty TwentyTwo) and recheck the field if it is still available. Then please activate plugins one by one and switch to your current theme to see where the field is registered (with code).