Every bookmaker caps payouts — per bet, per market, per customer per day — with limits varying by league and sport: top competitions carry the highest caps, obscure ones far lower. A 12-leg accumulator whose nominal payout exceeds the cap pays the cap, no matter what the slip multiplied to.
Check the cap before building anything lottery-shaped, and note which league on your coupon carries the LOWEST cap — mixed accumulators are capped by their weakest component at many books.
Slip says £2 × 8,000 = £16,000; the terms cap payouts on that league at £10,000. Six legs were mainstream but one Belarusian reserve-league pick dragged the whole coupon under the low-tier cap — the £6,000 difference was in the fine print all along.