If one of your display ad groups isn’t serving due to incorrect target and bid settings, what should you do?
Set the targeting for the ad group to “Broad Reach”
Set the targeting for the campaign to “Target all” and resubmit the ad
Set the targeting for the ad group to “Target all”
Set all targeting for the ad group to “Bid Only” and at least one targeting method to “Target and bid”
“Target and bid” restricts your ads to showing for the targeting method you’ve selected, like keywords.
When you add multiple targeting methods to the same ad group and set these to “Target and bid,” you’re telling AdWords to restrict or narrow the reach of your ads. When you add additional targeting methods and set them to “Bid only,” you’re telling AdWords not to restrict where your ads show but to increase or decrease its chances of showing depending on the bid you choose.
Read more here: https://support.google.com/adwords/answer/1209882?hl=en