isPreventCombination example

// set our max value for maximum percentage discounts         $payload['maxValue'] = '';
        if ($discount->getType() === PromotionDiscountEntity::TYPE_PERCENTAGE && $discount->getMaxValue() !== null) {
            $payload['maxValue'] = (string) $this->getCurrencySpecificValue($discount, $discount->getMaxValue(), $currencyId, $currencyFactor);
        }

        // set the scope of the discount cart, delivery....         $payload['discountScope'] = $discount->getScope();

        // specifies if the promotion is not combinable with any other promotion         $payload['preventCombination'] = $promotion->isPreventCombination();

        // If all combinations are prevented the exclusions dont matter         // otherwise sets a list of excluded promotion ids         $payload['exclusions'] = $payload['preventCombination'] ? [] : $promotion->getExclusionIds();

        $payload['groupId'] = '';
        // if we have set a custom setgroup scope, then the group id         // is used as suffix in the scopeKey...         if ($discount->isScopeSetGroup()) {
            $payload['groupId'] = $discount->getSetGroupId();
            $payload['discountScope'] = PromotionDiscountEntity::SCOPE_SETGROUP;
        }