I'd never heard of Z2U (I'm not a gamer) but they appear to be selling Shutterstock, Adobe Stock and iStock accounts and assets. I'm not sure if selling your account is contrary to agency terms (sort of like sub-leasing an apartment), but selling individual items is reselling what the agency licensed to you, and that's always against the agency terms even if they don't bother to chase up the offenders (search here for reports about Fiverr which has gigs reselling stock agency images)

https://www.z2u.com/shutterstock/accounts-5-16848

This is the platform's description of that category:

"The places where users buy Shutterstock Premium Account will generally be the site with the most users, for a number of reasons. One of which is that more sellers means more competition, which in turn, means lower prices as sellers compete to make sales. And it's important to find a reputable and trusted player-to-player trading platform since there are lots of scam sites out there that will not only steal your money, but also your personal data. We Z2U.com is the most secured trading platform for you! We always audit sellers' reputation and delivery speed, ensuring your buying safety! We take full responsibility for the entire selling and buying Shutterstock Image subscription, FLEX 25 mixed-asset subscription & On-demand packs"

https://www.z2u.com/adobe/accounts-5-16487?keywords=Adobe%20Stock

They have a lot of other offerings just for Creative Cloud subscriptions, not stock

https://www.z2u.com/istock/accounts-5-17471

"We Z2U.com have been in the industry of in-game asset exchange for over 10 years so we know how to attract the right sellers and drive a bargain. Here, you will find our sellers setting prices that allow you to pick out the best offer and review the sellers trust score, so you know you are dealing with someone worthwhile. All the products are provided by real users of iStock, 100% safe, no hack, no cheats! iStock Basic, Premium & Video Subscription Accounts for Sale, feel free to contact our 24/7 live support if you have any issues!"

I didn't find any mention of this platform when I searched here, so I have no idea if this has been brought to any agency's attention before, but I think anyone involved in this type of trading should have their agency account closed. At a minimum, the agencies should contact Z2U (who appear to be in China based on the country code of their WhatsApp number) to tell them they have to shut down these sales.

Has anyone had any dealings with this platform? Reviews are all over the place

https://www.trustpilot.com/review/www.z2u.com
https://www.reddit.com/r/Scams/comments/f1diwu/is_z2u_legit/
https://www.hackread.com/z2u-market-leak-expose-illicit-services-malware/