eBay API AddItemRequest PictureURL最终为空白图像

I'm using the AddItemRequest to add pictures to an eBay item's gallery and I can't seem to get the desired result. I got the code from a post on GitHub and have been referencing eBay's AddItem API Guide here.

<PictureDetails>
    <GalleryType>Plus</GalleryType>
    <PictureURL>http://i.ebayimg.com/00/s/MTA2NlgxNjAw/z/vF0AAOSwxH1T3cQb/$_1.JPG</PictureURL>
    <PictureURL>http://i.ebayimg.com/00/s/MTA2NlgxNjAw/z/odgAAOSwQItT3bxe/$_1.JPG</PictureURL>
</PictureDetails>

I've uploaded pictures to eBay's Picture Service (EPS) and used those URLs in the call, but when the item is listed there are two blank images in my gallery. What am I missing or doing wrong?

Be aware that pictures do not display in sandbox environment.

If this is not the case please paste the error message.