If products are approved in the promotion in Seller Center but not visible on the campaign page, the most likely scenario is that the campaign page is yet to load all of the items. This will happen in time and the products usually appear within 1-6 hours.
Sync times may vary depending on the number of products and the size of the campaign. If the issue persists beyond a day, please reach out to the Seller Help Desk and our team can review it.