Turn on the Carousel button just below the Creatives field to group all selected media into a single carousel ad. A carousel requires at least 2 and at most 10 media files, and you can mix images and videos in the cards. The order in which you select the files is kept in the cards: Meta doesn't reorder them. One carousel is created for each combination of selected account, campaign, and ad set. The URL is optional: if you leave it empty, the system inherits the link from the last ad in the ad set, or automatically uses the message destination in WhatsApp, Messenger, and Instagram Direct campaigns.