STPPaymentContext setup

import UIKit
import Stripe

class ExampleCheckoutViewController : UIViewController, STPPaymentContextDelegate {

    // MARK: Properties
    var customerContext = STPCustomerContext(keyProvider: API_Client.sharedInstance)
    var paymentContext : STPPaymentContext? = nil

    // MARK: UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()

        // initialize STPPaymentContext
        // Read more: https://stripe.com/docs/mobile/ios/standard#implement-your-apps-checkout-flow-using-stppaymentcontext
        self.paymentContext = STPPaymentContext(customerContext: self.customerContext, configuration: STPPaymentConfiguration.shared(), theme: STPTheme.default())
        self.paymentContext?.delegate = self
        self.paymentContext?.hostViewController = self

        // TODO: Set an amount below
        // self.paymentContext?.paymentAmount = ??
    }

    // MARK: Button actions

    // Present payment methods view controller via Payment Context
    func buttonAPressed() {
        self.paymentContext?.presentPaymentMethodsViewController()
    }

    // Request payment via Payment Context
    func buttonBPressed() {
        self.paymentContext?.requestPayment()
    }

    // MARK: STPPaymentContextDelegate
    /* Read more: https://stripe.com/docs/mobile/ios/standard#setting-the-delegate-and-host-view-controller */

    func paymentContextDidChange(_ paymentContext: STPPaymentContext) {
        // TODO: implement
    }

    func paymentContext(_ paymentContext: STPPaymentContext, didFailToLoadWithError error: Error) {
        // TODO: implement
    }

    func paymentContext(_ paymentContext: STPPaymentContext, didCreatePaymentResult paymentResult: STPPaymentResult, completion: @escaping STPErrorBlock) {
        // TODO: Send token to server to create a charge
    }

    func paymentContext(_ paymentContext: STPPaymentContext, didFinishWith status: STPPaymentStatus, error: Error?) {
        // TODO: implement
    }

}