Can't pull featured image from custom field? | CyberSEO Pro | Support Forum

So maybe I’m missing something really simple, but I can’t seem to pull the featured images from my posts on another blog. I’m using a theme called GoodStream on both blogs, where the featured image is stored in a custom field called ‘thumb’. I’ve checked the XML of my feed and the featured image section looks something like this:

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I have the option Post Thumbnail: Generate from the “thumb” custom field selected as well. Is there something I’m missing? Like a value I’m supposed to add in the custom field section of the XML syndicator?

I’m trying to pull posts from this sub-domain:
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to this main domain:
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