Two scenarios cause Facebook to review your ads:
You have made a new ad on Facebook. You have made changes to an available or existing ad. Changes that cause a review to consist of:
Altering creatives such as images, videos, text, or links. Changing your target audience. Select new billing events or goals. Often, your ad can be quickly approved, but again rejected after a day or two. It will be difficult to say the reason. The timing indicates that the initial approval was made by an automated process, and later a human reviews it manually and rejects the ad.