gotoPayment method

Implementation

void gotoPayment() {
  expandedIndex.value = 0;
  donationController.text = '\$ 0';
  currentDonation.value = 0;
  savedDonation.value = 0;
  hasConfirmedBooking.value = false;
  currentTab.value = 3;
  paymentExpireTimerCount.value = hasDiscountedFlight? 900: 480;
  paymentController.clearPage();
}