diff --git a/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php b/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
index b0b46b2..7d9d2c4 100644
--- a/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
+++ b/src/BusProNet/DataProcessor/PersonalDataSynchronizer.php
@@ -23,6 +23,9 @@ class PersonalDataSynchronizer
      * Processes all active participants (status 'F' or 'A'). Skips canceled participants (status 'S').
      * Updates all personal data fields and communication information.
      *
+     * For the applicant (index 0), missing mandatory fields are filled with defaults
+     * to handle company applicants created by travel agencies.
+     *
      * IMPORTANT: The applicant's address must never be modified. This method updates
      * participant addresses independently to ensure applicant data remains intact.
      *
@@ -37,6 +40,11 @@ class PersonalDataSynchronizer
                 continue;
             }
 
+            // Fill missing mandatory fields for applicant (company bookings by travel agencies)
+            if (0 === $participant->index) {
+                $this->fillMissingMandatoryFields($participant);
+            }
+
             $bookingData->participants[$participant->index]->firstName = $participant->firstName;
             $bookingData->participants[$participant->index]->name = $participant->lastName;
             $bookingData->participants[$participant->index]->dateOfBirth = $participant->dateOfBirth;
@@ -68,4 +76,34 @@ class PersonalDataSynchronizer
             }
         }
     }
+
+    /**
+     * Fills missing mandatory fields with defaults for company applicants.
+     *
+     * Travel agencies often create bookings with company data as the applicant,
+     * which lacks personal data fields. These fields are mandatory for the BPN
+     * API, so we fill them with sensible defaults.
+     */
+    private function fillMissingMandatoryFields(ParticipantDto $participant): void
+    {
+        if (null === $participant->firstName || '' === $participant->firstName) {
+            $participant->firstName = 'Anmelder';
+        }
+
+        if (null === $participant->gender || '' === $participant->gender) {
+            $participant->gender = 'D';
+        }
+
+        if (null === $participant->nationality || '' === $participant->nationality) {
+            $participant->nationality = 'D';
+        }
+
+        if (null === $participant->dateOfBirth) {
+            $participant->dateOfBirth = new \DateTimeImmutable('-20 years');
+        }
+
+        if (null === $participant->mobile || '' === $participant->mobile) {
+            $participant->mobile = '12345';
+        }
+    }
 }