I don't know about other customers, but I paid by bank transfer to account in the name of Lambda Investments via Wise.
Based on a simple Google search, most of the results for that nickname comes from Polish results.
Unless this is a nickname used by a lot of people, that would add up with what was previously posted on one of his websites about him actually being Polish:
It seems like quite a unique nickname though.
If we follow the trail of this nickname, we can also find the following:
View attachment 254525
Computer science student? Sounds like a background he could have, based on his skills.
The guy in the videos doesn't look like the guy in the photo from Sartre's websites though:
By following the name from this profile, you can find a lot of more information about a guy who's been a part of research papers on AI etc.:
https://bartoszzielinski.github.io/,
https://ieeexplore.ieee.org/author/37085359069