NativeCallsProtocol.swift

import Foundation
import UnityFramework

class UnityManager: NSObject {

    func launchUnity() {
        let isInitialized = self.ufw?.appController() != nil
        if isInitialized {
            self.ufw?.showUnityWindow()
        } else {
            guard let ufw = self.loadUnityFramework() else { return }
            self.ufw = ufw
            ufw.setDataBundleId(dataBundleId)
            ufw.register(self)
            ✅ NSClassFromString("FrameworkLibAPI")?.registerAPIforNativeCalls(self)
            ufw.runEmbedded(
                withArgc: CommandLine.argc,
                argv: CommandLine.unsafeArgv,
                appLaunchOpts: nil
            )
        }
    }
    ...
}

// From Unity
extension UnityManager: NativeCallsProtocol {
    
    func sendMessage(toMobileApp message: String!) {
        print(message)
    }
}