The StockXpert affiliate program was broken during a site upgrade and I recall someone official saying at the time that it wasn't going to be fixed, but I can't remember the source so I may be mistaken. That was before the JI sale, and I can't see Getty investing the time to get it back up and running.
I replaced my referral links with a non-referral link to the homepage back then, but I'm still getting referral click-throughs and signups. I have no idea where they're coming from.
My lifetime referral earnings at StockXpert is $1.50, but I write for photographers, not buyers. The StockXpert referral program doesn't pay anything for referred contributors, so those writing for buyers might have better luck.