The probe, Aug. 12 -- a trader flips a small bet into thousands on Polymarket, the screen showing what appears to be real winnings in real time. New York City Council Speaker Julie Menin said Wednesday at least some of those trades were staged, and she opened a formal investigation to find out how many.

Polymarket, Kalshi, Coinbase, and Gemini. The council says the platforms deployed a range of deceptive tactics, including videos depicting fake trades designed to resemble the platforms' own interfaces, undisclosed influencer marketing, and advertisements that showed "fictitious depictions of profitable wagers" that would in fact have generated losses. The council also alleged the platforms marketed to young people through potentially fal...