To change the default setting for delivery on asynchronous placements please go to: Settings -> Global Settings -> Advertiser -> Ad media >> Asynchronous ad media : "YES".
Please note here that if creative is set to "Yes", the creative will be delivered without any further system check on the asynchronous placement codes. If the ad is not asynchronous enabled, it will still be delivered. But either incorrectly or not displayed at all. This will inevitably lead to counting discrepancies. Therefore, we advise you to check the advertising media >> Is my creative capable of asycnrone?