Captured metafields are stored in this extension only, deduplicated by Shopify's own definition ID. The list page doesn't show namespace.key at all - rather than guess one, it's shown as "not captured" until you visit that field's detail page, which has the real value. Click any captured row to open its detail page in this tab (the popup stays open), or use "Capture all details" to walk through every missing one automatically - it keeps going even if you close this popup. Every row has a checkbox, checked by default - only checked rows are included in Copy/Download JSON and in "Capture all details".