You can think of internal fields as a master feed from which you can create any output feed. First you ‘map’ the fields from your store to our internal fields. Then you can use these internal fields to map every channel field:
How to map internal fields
3. Click Add internal field button to add more. You can name the additional fields yourself or you can select a field from the list:
Add as many internal fields as you can!
How to use internal fields to create your shopping feed
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