Appsflyer is a 3rd party tracking solution which provides tracking SDK and the purpose of tracking SDK is to track installs or conversions, report it to Appsflyer data center, then they verify the same and send a conversion postback to our server.
Please refer following useful articles from appsflyer help center:-
You may need to integrate Appsflyer tracking SDK which is required for iOS CPI campaigns and you can learn more about it at https://www.appsflyer.com
Note: Tracking SDK is optional for Android CPI campaigns
Appsflyer is 3rd party and for extended support, you may refer their help center (https://support.appsflyer.com) or simply contact their professional support team (firstname.lastname@example.org) for real help and guidance.