Hi JoesMimi,
Thanks for contributing. I am certainly not surprised that you can get the "zoom" feature to work by uploading your images directly to eBay, but that is not actually an indication that the problem causing the Auctiva hosted images that you submit as the header/gallery images not to reflect that option is due to something amiss on our side of things.
I have personally seen eBay's “zoom” feature on several listings I have posted using Auctiva hosted header/gallery images but, at the same time, I have also posted other listings using images with the exact same dimensions fail to reflect this feature on eBay.
The only *listing preference* that is required for the "zoom" feature to operate is eBay's Picture Pack feature and Picture Pack has been automatically included in all listings since eBay's began allowing sellers to add up to 12 header/gallery images to each listing at no cost in July.
If you submit a listing to eBay with externally hosted images, such as those hosted by Auctiva, eBay's system makes copies of those images to display in the header and gallery areas. Based on my observations, it seems like there must be an error that causes those copies not to reflect the “zoom” feature in some cases.
As such, I can only recommend that you contact eBay's customer support team for further clarification on why the feature is not showing up for you. Provided the images included with the listings are large enough to support the “zoom” feature, eBay should display it automatically.
-Mike