In a hypothetical two-leg accumulator, both legs must win. At decimal odds of 2.00 for each leg, the combined price is 4.00. A 1 unit stake returns 4.00 units including the original stake when both win. Under this defined example, a loss on either leg loses the entire stake; split wins and losses cannot be added as if these were separate bets. Multiplying those prices does not establish the chance of both outcomes happening. Related selections can share the same underlying match risks, so multiplying separate win probabilities requires an independence assumption that may be wrong. I would read the combination rules and identify what has to happen for a payout. This is a simplified example with no voids or partial settlements, not an offered bet or a recommendation.