Create new ad downloads the post's media and recreates it as a new ad (dark post): the ad starts from scratch, without the likes and comments of the original post. If the post is a carousel with several media items, the ad is also created as a carousel in the same order. Existing post uses the actual Instagram post as the ad, keeping its accumulated likes and comments. To use Existing post, the post must belong to the Instagram profile linked to the Page connected to the ad account. Note: Reels with licensed music can't be boosted in Existing post mode because of Meta's copyright restrictions.