feat: correct handling of vouchers

src/BusProNet/ApiClient.php

@@ -204,7 +204,7 @@ class ApiClient
             'user' => $this->config['bpn_username'],
             'key' => $this->createKey($this->config['bpn_username'], $this->config['bpn_password'], static::TYPE_BOOKING_UPDATE),
             'satz' => ['@typ' => static::TYPE_BOOKING_UPDATE],
-            'buchungsart' => 'Buchung',
+            'buchungsart' => Constants::BOOKING_TYPE_BOOKING,
             ...$payload,
         ];
 
@@ -228,7 +228,7 @@ class ApiClient
     {
         // Forcibly override booking status to generate inquiry payload
         $bookingDto->bookingStatus = 'A';
-        $payload = $this->bookingDataProcessor->createBookingRequestPayload($bookingDto, 'Anfrage');
+        $payload = $this->bookingDataProcessor->createBookingRequestPayload($bookingDto, Constants::BOOKING_TYPE_INQUIRY);
 
         $data = [
             'user' => $this->config['bpn_username'],
@@ -255,7 +255,7 @@ class ApiClient
      */
     public function createBooking(BookingDto $bookingDto, bool $debug = false): Notification|BookingResponse
     {
-        $payload = $this->bookingDataProcessor->createBookingRequestPayload($bookingDto, 'Buchung');
+        $payload = $this->bookingDataProcessor->createBookingRequestPayload($bookingDto, Constants::BOOKING_TYPE_BOOKING);
 
         $data = [
             'user' => $this->config['bpn_username'],