Sigbart error during prepare for segue/unwind segue

Question

I have an app where it is a marketplace and when you click on a product, it opens a detail view controller passing the data to display on the DetailVC. Additionally, inside the DetailVC, if you click on a button to claim the product, it segues to another VC to finalize the transaction.

In the DetailVC, there is a back button which is an unwind segue back to the main marketplace VC. Inside the TransactionVC, there is a cancel button which takes you back to the DetailVC.

When I am clicking the backButton in the DetailVC to take me back to the main market VC but I am getting a SIGBART Error and this :
020-07-15 09:05:23.707490-0500 evolutionatx[707:141952] Could not cast value of type 'evolutionatx.MarketplaceViewController' (0x1032c7868) to 'evolutionatx.PopUpPurchaseViewController' (0x1032c7ba8).

Here is the code for the DetailVC

import UIKit
import iCarousel
import CoreData

class MarketDetailViewController: UIViewController, UIScrollViewDelegate, iCarouselDelegate, iCarouselDataSource {   

var productImageArray = [UIImage]()
var productVideo = String()
var pointsToPurchase = String()
var productName = String()
var productDescription = String()
var companyLogo = UIImage()
var companyWebsite = String()
var additionalProductImage = [UIImage]()
var companyName = String()
var promoCODE = String()
var buyLink = String()
var slides:[Slide] = [];

//IB
@IBOutlet weak var productNameLabel: UILabel!
@IBOutlet weak var productPriceLabel: UILabel!
@IBOutlet weak var productDescLabel: UILabel!
@IBOutlet weak var claimButton: UIButton!
@IBOutlet weak var imgScrollView: UIScrollView!
@IBOutlet weak var websiteButton: UIButton!
@IBOutlet weak var pageControl: UIPageControl!
@IBOutlet weak var logoDisplay: UIImageView!
@IBOutlet weak var carouselView: iCarousel!
@IBOutlet weak var otherProductslabe: UILabel!

var carouselImages = [UIImage]()
var evoCoin = Int()

override func awakeFromNib() {
    super.awakeFromNib()
    carouselImages = productImageArray
}
override func viewDidLoad() {
    super.viewDidLoad()
    valueSetter()
    
    imgScrollView.delegate = self
    slides = createSlides()
    
    setupSlideScrollView(slides: slides)
    
    pageControl.numberOfPages = slides.count
    pageControl.currentPage = 0
    
    view.bringSubviewToFront(pageControl)
}
    }
    
func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let pageIndex = round(scrollView.contentOffset.x/view.frame.width)
        pageControl.currentPage = Int(pageIndex)
        
        let maximumHorizontalOffset: CGFloat = scrollView.contentSize.width - scrollView.frame.width
        let currentHorizontalOffset: CGFloat = scrollView.contentOffset.x
        
        // vertical
        let maximumVerticalOffset: CGFloat = scrollView.contentSize.height - scrollView.frame.height
        let currentVerticalOffset: CGFloat = scrollView.contentOffset.y
        
        let percentageHorizontalOffset: CGFloat = currentHorizontalOffset / maximumHorizontalOffset
        let percentageVerticalOffset: CGFloat = currentVerticalOffset / maximumVerticalOffset        
    }

@IBAction func claimProduct(_ sender: Any) {
    print("tap rec")
    claimProductandPurchase()        
}

func claimProductandPurchase(){

    evoCOiner()
    if(evoCoin >= Int(pointsToPurchase)!){
        print("Transaction Successful")
        performSegue(withIdentifier: "proceedQuestion", sender: self)
    }
    else{
        showToast(controller: self, message: "Insufficient EvoCoins", seconds: 0.5)
    }       
}

func showToast(controller: UIViewController, message : String, seconds: Double) {
    let alert = UIAlertController(title: nil, message: message, preferredStyle: .alert)
    alert.view.backgroundColor = UIColor.black
    alert.view.alpha = 0.6
    alert.view.layer.cornerRadius = 15

    controller.present(alert, animated: true)

    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + seconds) {
        alert.dismiss(animated: true)
    }
}

func evoCoiner(){
    
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "EvoCoins")
    request.returnsObjectsAsFaults = false
    do{
        let result = try context.fetch(request)
        for data in result as! [NSManagedObject]
        {
            evoCoin = data.value(forKey: "evoCoins") as! Int
        }
    }catch{
        print("Failed")
    }
}    
 override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    let detailController = segue.destination as! PopUpPurchaseViewController
        detailController.ppromo = promoCODE
        detailController.link = buyLink
        detailController.coinToPurchase = Int(pointsToPurchase)!
}
    
//This is the unwind used by the transaction back button
@IBAction func unwindToItem(segue: UIStoryboardSegue) {
}
}

Here is the code in the transaction VC

import UIKit
import AMTabView
import CoreData

class MarketplaceViewController: UIViewController, TabItem {

@IBOutlet weak var sView: UIView!

@IBOutlet weak var evoCoinLabe: UILabel!
    
 //For the sake of simplicity I only kept the Unwind functions    
  //MARK: - UNWIND FUNCTIONS
   @IBAction func unwindToMainMarketView(segue: UIStoryboardSegue) {
   }
   }

How can I fix this error?

Please advise if my question was not clear or properly phrased (if so, sorry I am pretty new to all of this)

Answer 1

As @matt already said in his comment and the error clearly states, you cannot cast a MarketplaceViewController to a PopUpPurchaseViewController.

Furthermore instead of doing a forced cast, always look for a safe one like below. Doing so will prevent crashes.

if let detailController = segue.destination as? PopUpPurchaseViewController {
    ...
}
else { 
    // log failed to cast
}