Ad auction is the process that runs the best ads based on the ads’ maximum bids and performance. In the auction process, all Facebook ads compete against one another, and the ads that the system determines will be the most successful will be shown.
If you’d like to make your ad more competitive in the auction, raise your bid. Advertisers are only charged if the bid is necessary to win the auction. The bid that wins may be lower than the maximum bid you have set for your ads, so it is recommended that you enter your true maximum bid. This will decrease the likelihood of missing clicks or impressions. It is also recommended that you target a relevant audience who are more likely to engage with your ads.