(Resolved) Had few issue on BE: Make sure your endpoint on you server-side has "/" in the end e.g. /.well-known/appattribution/report-attribution/ On server-side we expected to hit request with "www", seems like it's being cut-off in the middle, although in the apps plist we explicitly included that On the advertised app: Have to add Postback update, i did it in "didFinishLaunchingWithOptions" Task { if #available(iOS 17.4, *) { try await Postback.updateConversionValue(1, lockPostback: true) } else { // Fallback on earlier versions } } And my testing steps be like: iOS Settings -> Developer -> Development postbacks -> Configure & Create postback Run you app with xcode When app launched, open "Development Postbacks" again and push "Transmit Development Postbacks" Success -> request is visible with proxy tool and have Console log "Found 1 postbacks eligible for transmission for environments: "