Hi Sam,
Thank you for reaching out. As you can see in the Display Name and XML Attribute of this field, the FeedItemId is the itemId.
Thanks and regards,
Xiaoming, Google Ads API Team
Hi Sam,
Thank you for reaching out. It could be that the feed only contains ad extensions. You would be able to get the Extension Feed Item ID by querying the extension_feed_item.id from the extension_feed_item resource in the Google Ads API.
Thanks and regards,
Xiaoming, Google Ads API Team