Cannot find type 'configuration' in scope

Hi, I am following this github link - https://github.com/stripe-samples/firebase-mobile-payments and thid https://github.com/stripe/stripe-ios/blob/21.8.1/Stripe/PaymentSheet.swift#L33-L152 . It shows error - "cannot find configuration in scope" and other errors as shown below-

 import UIKit
  import Foundation
     public class PaymentSheet {
/// This contains all configurable properties of PaymentSheet
public let configuration: Configuration // Error - Cannot find type 'Configuration' in scope

/// The most recent error encountered by the customer, if any.
public private(set) var mostRecentError: Error?

/// Initializes a PaymentSheet
/// - Parameter paymentIntentClientSecret: The [client secret](https://stripe.com/docs/api/payment_intents/object#payment_intent_object-client_secret) of a Stripe PaymentIntent object
/// - Note: This can be used to complete a payment - don't log it, store it, or expose it to anyone other than the customer.
/// - Parameter configuration: Configuration for the PaymentSheet. e.g. your business name, Customer details, etc.
public convenience init(paymentIntentClientSecret: String, configuration: Configuration) { // Error - Cannot find type 'Configuration' in scope

    self.init(
        intentClientSecret: .paymentIntent(clientSecret: paymentIntentClientSecret),//Error - Cannot infer contextual base in reference to member 'paymentIntent'
        configuration: configuration
    )
}

/// Initializes a PaymentSheet
/// - Parameter setupIntentClientSecret: The [client secret](https://stripe.com/docs/api/setup_intents/object#setup_intent_object-client_secret) of a Stripe SetupIntent object
/// - Parameter configuration: Configuration for the PaymentSheet. e.g. your business name, Customer details, etc.
public convenience init(setupIntentClientSecret: String, configuration: Configuration) { // Error - Cannot find type 'Configuration' in scope
    self.init(
        intentClientSecret: .setupIntent(clientSecret: setupIntentClientSecret),//Error - Cannot infer contextual base in reference to member 'setupIntent
        configuration: configuration
    )
}

required init(intentClientSecret: IntentClientSecret, configuration: Configuration) {// Error - Cannot find type 'Configuration' in scope

    STPAnalyticsClient.sharedClient.addClass(toProductUsageIfNecessary: PaymentSheet.self)// Error - Cannot find 'STPAnalyticsClient' in scope
    self.intentClientSecret = intentClientSecret
    self.configuration = configuration
    STPAnalyticsClient.sharedClient.logPaymentSheetInitialized(configuration: configuration)
}

/// Presents a sheet for a customer to complete their payment
/// - Parameter presentingViewController: The view controller to present a payment sheet
/// - Parameter completion: Called with the result of the payment after the payment sheet is dismissed
@available(iOSApplicationExtension, unavailable)
@available(macCatalystApplicationExtension, unavailable)
public func present(
    from presentingViewController: UIViewController,
    completion: @escaping (PaymentSheetResult) -> () //Error - Cannot find type 'PaymentSheetResult' in scope
) {
    // Overwrite completion closure to retain self until called
    let completion: (PaymentSheetResult) -> () = { status in
        // Dismiss if necessary
        if self.bottomSheetViewController.presentingViewController != nil {
            self.bottomSheetViewController.dismiss(animated: true) {
                completion(status)
            }
        } else {
            completion(status)
        }
        self.completion = nil
    }
    self.completion = completion

    // Guard against basic user error
    guard presentingViewController.presentedViewController == nil else {
        assertionFailure("presentingViewController is already presenting a view controller")
        let error = PaymentSheetError.unknown( // Error - annot find 'PaymentSheetError' in scope
            debugDescription: "presentingViewController is already presenting a view controller"
        )
        completion(.failed(error: error))
        return
    }

    // Configure the Payment Sheet VC after loading the PI/SI, Customer, etc.
    PaymentSheet.load(
        apiClient: configuration.apiClient,
        clientSecret: intentClientSecret,
        ephemeralKey: configuration.customer?.ephemeralKeySecret,
        customerID: configuration.customer?.id
    ) { result in
        switch result {
        case .success((let intent, let paymentMethods)):
            // Set the PaymentSheetViewController as the content of our bottom sheet
            let isApplePayEnabled = StripeAPI.deviceSupportsApplePay() && self.configuration.applePay != nil
            let paymentSheetVC = PaymentSheetViewController(
                intent: intent,
                savedPaymentMethods: paymentMethods,
                configuration: self.configuration,
                isApplePayEnabled: isApplePayEnabled,
                delegate: self
            )
            // Workaround to silence a warning in the Catalyst target
            #if targetEnvironment(macCatalyst)
            self.configuration.style.configure(paymentSheetVC)
            #else
            if #available(iOS 12.0, *) {
                self.configuration.style.configure(paymentSheetVC)
            }
            #endif
            self.bottomSheetViewController.contentStack = [paymentSheetVC]
        case .failure(let error):
            completion(.failed(error: error))
        }
    }

    presentingViewController.presentPanModal(bottomSheetViewController)// Error - Value of type 'UIViewController' has no member 'presentPanModal'
}

// MARK: - Internal Properties
/// An unordered list of paymentMethod types that can be used with PaymentSheet
static let supportedPaymentMethods: [STPPaymentMethodType] = [.card, .iDEAL]// Error - Cannot find type 'STPPaymentMethodType' in scope

let intentClientSecret: IntentClientSecret//. Error -  Cannot find type 'IntentClientSecret' in scope

var completion: ((PaymentSheetResult) -> ())?//  Error -   Cannot find type 'PaymentSheetResult' in scope  
lazy var bottomSheetViewController:    BottomSheetViewController = {
    let vc = BottomSheetViewController(
        contentViewController:   LoadingViewController(delegate: self)
    )
    if #available(iOS 12.0, *) {
        configuration.style.configure(vc)
    }
    return vc
}()

  }

How should I sort it out ?