So, after 30th September, Facebook Ads is bid only
What is bidding?
We’ve seen high adoption of and strong results from bidding. Audience Network is on track to have 50% of revenue transacted through bidding before the end of 2020, so while Apple’s changes greatly accelerate the transition timeline, our bidding focus continues a trend already benefiting a significant number of publishers.
Bidding has proven to help publishers maximize their revenue and increase operational efficiency versus waterfall. In our recent report, The New Era in Ad Monetization: How App Bidding is Transforming Businesses, we’ve seen businesses experience up to a 27% increase in average revenue per daily active user (ARPDAU). Further, publishers report reducing time spent on ad operations by up to 50% as a result of moving from waterfall to bidding.
Industry analysts also note bidding’s positive impact on publishers and the ad ecosystem. In IDC’s The Current State of Header Bidding and In-App Bidding, Karsten Weide, VP Advertising, IDC says, “Bidding helps democratize the auction process, allowing publishers to work with more marketers, in terms of both total number and variety of sources. The model also allows publishers to increase their inventory revenue yield and fill rates.”
(Taken from https://www.facebook.com/audiencenetwork/resources/blog/audience-network-to-become-bidding-only-beginning-with-ios-in-2021)
What must I do?
Now u can use Bid to maximize your app revenue
Supported for FB Mediation
Ironsource Ads : Setted Up 
More networks Coming soon.....