First, PredictIt issues a 1099 on net income. They remove your investment for you automatically. IT IS NOT CONSIDERED GAMBLING. https://predictit.freshdesk.com/support/solutions/articles/5000692877-how-do-you-calculate-a-trader-s-net-profit-for-tax-reporting-purposes-
Second, while all gambling gains are reportable, only large wins get automatically reported (>$1200 or 100/1, I believe, depending on format). These are generally reported on a Form W-2G, not a Form 1099. You may deduct gambling losses against your reported win IF you itemize deductions (if you take the standard deduction, you’re out of luck). Further, if you are a professional gambler (i.e. as a primary source of income) you may deduct all losses, even beyond your winnings (but none of us are professional gamblers, so don’t try that).