Is there any ad serving third party platform that integrates with Squarespace?

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Is there any ad serving third party platform that integrates with Squarespace that'll let my client track, rotate, and run their own ads, without joining an ad network? (So not Adsense). The aim is to run more than one ad in an ad space. My client currently sells Leaderboards and MPU space that I set up, but these ads run one banner at a time, for example. They are looking for an integration where they can run two banners in the same space, so the ad changes when the page is refreshed, for example. Thanks, Beth