Here are a few factors that may influence your ad delivery:
- Your ad may still be under review. Before your ads are published to Facebook or Instagram, the Facebook system reviews them to ensure they meet the Advertising Policies. You can see the status of your ad in the Delivery column of Ads Manager. Most ads are reviewed within 24 hours, although in some cases it may take longer. The ad usually started delivery after being approved.
- Your ads may have been turned off because you've reached the account spending limit you set for your ad account. To continue to run your ads, you can reset or change your limit.
(Learn more about Facebook account spending limit: https://www.facebook.com/business/help/320646548127581)
Your retargeting audience may not be enough so your campaign can not be delivered by the Facebook system. To deliver Facebook DPA retargeting, it generally needs at least hundreds of daily unique visitors who have viewed your product pages. I would suggest you gain more traffic by spending a bit of budget on traffic-driven ads, and then those people can be collected as your retargeting audience. Generally, the larger your retargeting audience is, the better the result your retargeting ad will achieve.