diff --git a/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php b/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
index 12de4f5..33c9d10 100644
--- a/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
+++ b/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
@@ -33,7 +33,7 @@ class PersonalDataSynchronizer
      *
      * @param array<ParticipantDto> $participants            The participants array from the form
      * @param Booking               $bookingData             The booking data object to update
-     * @param bool                  $isInternalAgencyBooking Whether to fill default names for canceled participants
+     * @param bool                  $isInternalAgencyBooking Whether to fill default names for participants with empty names
      */
     public function updateParticipantPersonalData(
         array $participants,
@@ -48,20 +48,18 @@ class PersonalDataSynchronizer
             $bookingData->participants[$participant->index]->firstName = $participant->firstName;
             $bookingData->participants[$participant->index]->name = $participant->lastName;
 
-            // For internal agency bookings, canceled participants with empty names get default values
-            // since they are read-only in the UI and cannot be fixed by applicants
+            // For internal agency bookings, participants with empty names get default values.
+            // Agencies pre-book slots with placeholder data (e.g. applicant surname, empty first name),
+            // and the BPN API rejects updates with empty name fields.
             if ($isInternalAgencyBooking) {
-                $status = $bookingData->participantsStatus[$participant->index] ?? null;
-                if ('S' === $status) {
-                    $defaultName = sprintf('Teilnehmer:in %d', $participant->index + 1);
-                    $personalData = $bookingData->participants[$participant->index];
+                $defaultName = sprintf('Teilnehmer:in %d', $participant->index + 1);
+                $personalData = $bookingData->participants[$participant->index];
 
-                    if (null === $personalData->firstName || '' === $personalData->firstName) {
-                        $personalData->firstName = $defaultName;
-                    }
-                    if (null === $personalData->name || '' === $personalData->name) {
-                        $personalData->name = $defaultName;
-                    }
+                if (null === $personalData->firstName || '' === $personalData->firstName) {
+                    $personalData->firstName = $defaultName;
+                }
+                if (null === $personalData->name || '' === $personalData->name) {
+                    $personalData->name = $defaultName;
                 }
             }
 
diff --git a/tests/BusProNet/DataProcessor/BookingDataProcessorTest.php b/tests/BusProNet/DataProcessor/BookingDataProcessorTest.php
index adfe277..d6633d0 100644
--- a/tests/BusProNet/DataProcessor/BookingDataProcessorTest.php
+++ b/tests/BusProNet/DataProcessor/BookingDataProcessorTest.php
@@ -564,6 +564,132 @@ class BookingDataProcessorTest extends TestCase
         $this->assertEquals('', $canceledParticipant->name);
     }
 
+    public function testConfirmedParticipantEmptyNamesFilledForAgencyBooking(): void
+    {
+        $formData = $this->createFormDataWithConfirmedParticipantEmptyNames();
+
+        $this->processor->createUpdateRequestPayload($formData);
+
+        // Confirmed participant (index 1) with empty names should have default names filled
+        $participant = $formData->booking->participants[1];
+        $this->assertEquals('Teilnehmer:in 2', $participant->firstName);
+        $this->assertEquals('Teilnehmer:in 2', $participant->name);
+
+        // Active participant (index 0) should retain original names from form
+        $activeParticipant = $formData->booking->participants[0];
+        $this->assertEquals('Participant0', $activeParticipant->firstName);
+        $this->assertEquals('LastName', $activeParticipant->name);
+    }
+
+    public function testConfirmedParticipantPartialEmptyNameFilledForAgencyBooking(): void
+    {
+        $formData = $this->createFormDataWithConfirmedParticipantPartialEmptyName();
+
+        $this->processor->createUpdateRequestPayload($formData);
+
+        // Participant with lastName but empty firstName should get default firstName only
+        $participant = $formData->booking->participants[1];
+        $this->assertEquals('Teilnehmer:in 2', $participant->firstName);
+        $this->assertEquals('Schnekenburger', $participant->name);
+    }
+
+    private function createFormDataWithConfirmedParticipantEmptyNames(): BookingDto
+    {
+        $bookingDto = new BookingDto($this->createMockTravel(), 1);
+        $bookingDto->booking = $this->createMockBookingWithEmptyNameParticipant('F', '', '');
+        $bookingDto->agencyCode = '0004';
+        $bookingDto->participants = [
+            $this->createMockParticipantDto(0, 'F'),
+            $this->createMockParticipantDtoWithEmptyNames(1, 'F'),
+        ];
+
+        return $bookingDto;
+    }
+
+    private function createFormDataWithConfirmedParticipantPartialEmptyName(): BookingDto
+    {
+        $bookingDto = new BookingDto($this->createMockTravel(), 1);
+        $bookingDto->booking = $this->createMockBookingWithEmptyNameParticipant('F', '', 'Schnekenburger');
+        $bookingDto->agencyCode = '0004';
+        $bookingDto->participants = [
+            $this->createMockParticipantDto(0, 'F'),
+            $this->createMockParticipantDtoWithPartialName(1, 'F', '', 'Schnekenburger'),
+        ];
+
+        return $bookingDto;
+    }
+
+    private function createMockBookingWithEmptyNameParticipant(
+        string $status,
+        string $firstName,
+        string $lastName,
+    ): Booking {
+        $booking = new Booking();
+        $booking->id = 123;
+        $booking->status = 'ACTIVE';
+        $booking->agencyId = 999;
+        $booking->dateId = 1;
+        $booking->hotelId = 1;
+        $booking->paymentId = '1';
+        $booking->paymentLabel = 'Credit Card';
+        $booking->paymentType = 'CC';
+        $booking->additionalServices = [];
+        $booking->transportationServices = [];
+        $booking->pickups = [];
+        $booking->dropOffs = [];
+
+        $emptyNameParticipant = new PersonalData();
+        $emptyNameParticipant->firstName = $firstName;
+        $emptyNameParticipant->name = $lastName;
+        $emptyNameParticipant->dateOfBirth = new \DateTimeImmutable('1990-01-01');
+        $emptyNameParticipant->gender = 'M';
+        $emptyNameParticipant->nationality = 'DE';
+        $emptyNameParticipant->address = new Address();
+        $emptyNameParticipant->communication = new Communication();
+
+        $booking->participants = [
+            $this->createMockPersonalData('Participant0'),
+            $emptyNameParticipant,
+        ];
+        $booking->participantsStatus = ['F', $status];
+        $booking->applicant = $this->createMockPersonalData('Applicant');
+        $booking->bankAccount = null;
+        $booking->rooms = [];
+
+        return $booking;
+    }
+
+    private function createMockParticipantDtoWithPartialName(
+        int $index,
+        string $status,
+        string $firstName,
+        string $lastName,
+    ): ParticipantDto {
+        $participant = new ParticipantDto();
+        $participant->index = $index;
+        $participant->status = $status;
+        $participant->firstName = $firstName;
+        $participant->lastName = $lastName;
+        $participant->dateOfBirth = new \DateTimeImmutable('1990-01-01');
+        $participant->gender = 'M';
+        $participant->nationality = 'DE';
+        $participant->height = '175';
+        $participant->weight = '70';
+        $participant->shoeSize = '40';
+        $participant->email = null;
+        $participant->mobile = null;
+        $participant->courses = [];
+        $participant->additionalServices = [];
+        $participant->skiPass = null;
+        $participant->board = [];
+        $participant->rentals = [];
+        $participant->transportationOutbound = $this->createMockService(1);
+        $participant->transportationInbound = $this->createMockService(2);
+        $participant->pickup = null;
+
+        return $participant;
+    }
+
     private function createFormDataWithCanceledParticipantEmptyNames(): BookingDto
     {
         $bookingDto = new BookingDto($this->createMockTravel(), 1);