Biometric Authentication evaluation with swiftUI

I've been able to get a rudimentary version of Face / Touch ID working inside my app. However, I want to add better fallbacks and error handling.

So I've been researching how to do it. There are fantastic resources like this:

Face ID evaluation process not working properly

However, I can't find anything that works inside a SwiftUI view. At the moment my project won't run with:

'unowned' may only be applied to class and class-bound protocol types, not 'AuthenticateView'

and

Value of type 'AuthenticateView' has no member 'present'

any help would be much appreciated. Thank you!

Here's my code inside AuthenticateView.swift

func Authenticate(completion: @escaping ((Bool) -> ())){    //Create a context    let authenticationContext = LAContext()    var error:NSError?    //Check if device have Biometric sensor    let isValidSensor : Bool = authenticationContext.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)    if isValidSensor {        //Device have BiometricSensor        //It Supports TouchID        authenticationContext.evaluatePolicy(            .deviceOwnerAuthenticationWithBiometrics,            localizedReason: "Touch / Face ID authentication",            reply: { [unowned self] (success, error) -> Void in                if(success) {                    // Touch / Face ID recognized success here                    completion(true)                } else {                    //If not recognized then                    if let error = error {                        let strMessage = self.errorMessage(errorCode: error._code)                        if strMessage != ""{                            self.showAlertWithTitle(title: "Error", message: strMessage)                        }                    }                    completion(false)                }        })    } else {        let strMessage = self.errorMessage(errorCode: (error?._code)!)        if strMessage != ""{            self.showAlertWithTitle(title: "Error", message: strMessage)        }    }}

func errorMessage(errorCode:Int) -> String{    var strMessage = ""    switch errorCode {    case LAError.Code.authenticationFailed.rawValue:        strMessage = "Authentication Failed"    case LAError.Code.userCancel.rawValue:        strMessage = "User Cancel"    case LAError.Code.systemCancel.rawValue:        strMessage = "System Cancel"    case LAError.Code.passcodeNotSet.rawValue:        strMessage = "Please goto the Settings & Turn On Passcode"    case LAError.Code.touchIDNotAvailable.rawValue:        strMessage = "TouchI or FaceID DNot Available"    case LAError.Code.touchIDNotEnrolled.rawValue:        strMessage = "TouchID or FaceID Not Enrolled"    case LAError.Code.touchIDLockout.rawValue:        strMessage = "TouchID or FaceID Lockout Please goto the Settings & Turn On Passcode"    case LAError.Code.appCancel.rawValue:        strMessage = "App Cancel"    case LAError.Code.invalidContext.rawValue:        strMessage = "Invalid Context"    default:        strMessage = ""    }    return strMessage}

func showAlertWithTitle( title:String, message:String ) {    let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)    let actionOk = UIAlertAction(title: "OK", style: .default, handler: nil)    alert.addAction(actionOk)    self.present(alert, animated: true, completion: nil)}