I bet 4.5k on PredictIt with a spread of; likely Biden states (WI, MI, MN), Biden prez and popular vote. To pick my bets I used the Kelly betting algorithm with 538 stats and PredictIt's fees included. I only bet on the races with an kelly fraction (F) of .5 or more. The average F of the bets was .7. The spread would break even if Biden narrowly lost (Trump wins AZ, PA, GA, NC, FL), and only return negative with a major poll error of 8 points in the Great Lakes. Therefore I was watching FL for a large polling error.
After FL results came in I attempted to sell my Biden prez tix. PredictIt crashed, but I was among the first to refresh the page and sold my Biden tix at pre-election value of .66. Biden tix fell to .20 at 10:00 pm and I bought 1000 at .12 because I knew the redshift in Michigan was skewing the results. In total I gained about 20% on my portfolio over the night.
FTX fees are .07% per trade if you take liquidity or 0 if you add liquidity. I paid somewhere under 1% to get the money from IBKR into my bank then into Coinbase then into FTX.
Betting on FTX is not allowed for US residents. I'm a US person but not a US resident, which gives me more options for prediction markets than most people. I heard some US residents were betting on Catnip. While FTX is a web site that lets people trade cryptocurrency balances held by FTX, Catnip is a decentralized market, so in some sense it's more of a "real" crypto betting market than FTX.