Как исправить ошибку «Невозможно прочитать свойство неопределенного» в почтовом запросе Angular

Я получаю эти ошибки, и я не знаю, как это исправить. Я делаю форму, которая будет делать почтовый запрос к API.

ОШИБКА TypeError: Не удается прочитать свойство «электронная почта» неопределенного

ОШИБКА TypeError: Не удается прочитать свойство «paymentMethod» неопределенного

Я ожидаю:

createdBy: string from email input,
paymentMethod: string from paymentMethod select input,

Но что я получаю:

createdBy: null,
paymentMethod: null

Интерфейсы

export interface BillingForm {
    fullName: string;
    email: string;
    address: string;
    city: string;
    paymentMethod: string;

  }

export interface Order {
  id?: number;
  companyId: number;
  created: string;
  createdBy: string;
  paymentMethod: string;
  totalPrice: number;
  status: number;
  orderRows: OrderRows[];
}

сервис.тс

public postOrder(order: Order): Observable<Order> {
      console.info(order);
      return this.http.post<Order>(this.ordersURL, order, httpOptions).pipe(
        catchError(this.handleError('postOrder', order))
      );

компонент.ts

ngOnInit() {

    this.shippingForm = this.formBuilder.group({
      name: ['', Validators.required],
      email: ['', Validators.required],
      address: ['', Validators.required],
      paymentMethod: ['', Validators.required],
      city: ['', Validators.required],
    })
  }


  onSubmit(billingForm: BillingForm) {
    const order = this.newOrder(billingForm);

    this.productService.postOrder(order).subscribe (
      response => console.info('success', response),
      error => console.info('error', error)
    )

    this.submitted = true;

    if (this.shippingForm.invalid) {
      return;
    }
    this.success = true;

  }

  newOrder(billingForm: BillingForm ): Order {
    return {
      companyId: 6,
      created: moment().locale("sv").format("YYYY-MM-DDTLTS"),
      createdBy: billingForm.email,
      paymentMethod: billingForm.paymentMethod,
      totalPrice: this.totalPrice,
      status: 0,
      orderRows: this.orderRows

    }
  }

  get email() {
    return this.shippingForm.get("email") as FormControl;
  }

  get paymentMethod() {
    return this.shippingForm.get("paymentMethod") as FormControl;
  }   

компонент.html

<form [formGroup] = "shippingForm" (ngSubmit) = "onSubmit(billingForm)">
        <h5 *ngIf = "success">Your form is valid!</h5>
          <div class = "form-group col-md-6">
            <label for = "inputEmail">Email</label>
            <input type = "email" formControlName = "email" class = "form-control" id = "inputEmail" placeholder = "Email">
            <div *ngIf = "submitted && shippingForm.controls.email.errors" class = "error">
              <div *ngIf = "shippingForm.controls.email.errors.required">Your email is required!</div>
            </div>
          </div>
        </div>
        <div class = "form-group col-md-6">
            <label for = "payment">Payment Method: </label>
            <select type = "select" formControlName = "paymentMethod" class = "form-control" id = "payment"
              aria-placeholder = "Mastercard">
              <option selected> Choose...</option>
              <option *ngFor = "let paymentMethod of paymentMethods">
                {{ paymentMethod }}
              </option>
            </select>
            <div *ngIf = "submitted && shippingForm.controls.paymentMethod.errors" class = "error">
              <div *ngIf = "shippingForm.controls.paymentMethod.errors.required">Your preferred payment method is required!</div>
            </div>
          </div>
</form>