diff --git a/app/Domains/CostUnit/Actions/ChangeCostUnitDetails/ChangeCostUnitDetailsCommand.php b/app/Domains/CostUnit/Actions/ChangeCostUnitDetails/ChangeCostUnitDetailsCommand.php
index 341b025..b687759 100644
--- a/app/Domains/CostUnit/Actions/ChangeCostUnitDetails/ChangeCostUnitDetailsCommand.php
+++ b/app/Domains/CostUnit/Actions/ChangeCostUnitDetails/ChangeCostUnitDetailsCommand.php
@@ -14,7 +14,7 @@ class ChangeCostUnitDetailsCommand {
 
         $this->request->costUnit->distance_allowance = $this->request->distanceAllowance->getAmount();
         $this->request->costUnit->mail_on_new = $this->request->mailOnNew;
-        $this->request->costUnit->billing_deadline = $this->request->billingDeadline;
+        $this->request->costUnit->billing_deadline = $this->request->billingDeadline?->format('Y-m-d');
 
         $response->success = $this->request->costUnit->save();
         return $response;
diff --git a/app/Domains/CostUnit/Actions/CreateCostUnit/CreateCostUnitCommand.php b/app/Domains/CostUnit/Actions/CreateCostUnit/CreateCostUnitCommand.php
index 93129f5..ea7617a 100644
--- a/app/Domains/CostUnit/Actions/CreateCostUnit/CreateCostUnitCommand.php
+++ b/app/Domains/CostUnit/Actions/CreateCostUnit/CreateCostUnitCommand.php
@@ -17,7 +17,7 @@ class CreateCostUnitCommand {
             'name' => $this->request->name,
             'tenant' => currentTenant()->slug,
             'type' => $this->request->type,
-            'billing_deadline' => $this->request->billingDeadline,
+            'billing_deadline' => $this->request->billingDeadline?->format('Y-m-d'),
             'distance_allowance' => $this->request->distanceAllowance->getAmount(),
             'mail_on_new' => $this->request->mailOnNew,
             'allow_new' => true,
diff --git a/app/Domains/CostUnit/Controllers/EditController.php b/app/Domains/CostUnit/Controllers/EditController.php
index 9bc5192..e3605ce 100644
--- a/app/Domains/CostUnit/Controllers/EditController.php
+++ b/app/Domains/CostUnit/Controllers/EditController.php
@@ -37,7 +37,10 @@ class EditController extends CommonController{
 
         $saveParams = $request->get('formData');
         $distanceAllowance = Amount::fromString($saveParams['distanceAllowance']);
-        $billingDeadline = isset($saveParams['billingDeadline']) ? \DateTime::createFromFormat('Y-m-d', $saveParams['billingDeadline']) : null;
+        $rawBillingDeadline = $saveParams['billingDeadline'] ?? null;
+        $billingDeadline = !empty($rawBillingDeadline)
+            ? (\DateTime::createFromFormat('!Y-m-d', $rawBillingDeadline) ?: null)
+            : null;
 
         $request = new ChangeCostUnitDetailsRequest($costUnit, $distanceAllowance, $saveParams['mailOnNew'], $billingDeadline);
         $command = new ChangeCostUnitDetailsCommand($request);
diff --git a/app/Domains/Invoice/Controllers/SaveInvoiceController.php b/app/Domains/Invoice/Controllers/SaveInvoiceController.php
index 649958d..df1c8e8 100644
--- a/app/Domains/Invoice/Controllers/SaveInvoiceController.php
+++ b/app/Domains/Invoice/Controllers/SaveInvoiceController.php
@@ -26,6 +26,18 @@ class SaveInvoiceController extends CommonController
             ]);
         }
 
+        // Sicherheitsnetz hinter der Oberfläche: Wer gereist ist, steht im Zahlungsgrund auf Beleg und EüR und
+        // ist bei Fahrtkosten Pflicht. Geprüft wird hier und nicht im Command, weil auch Abrechnungskorrekturen
+        // durch den Command laufen -- sie bringen ihren Zahlungsgrund mit, aber keine Personen. Und vor dem
+        // Upload, damit eine abgelehnte Einreichung keinen verwaisten Beleg hinterlässt.
+        if ($invoiceType === InvoiceType::INVOICE_TYPE_TRAVELLING
+            && Validator::make($request->all(), ['travellers' => 'required|string'])->fails()) {
+            return response()->json([
+                'status' => 'error',
+                'message' => 'Bitte gib an, welche Personen gereist sind.'
+            ]);
+        }
+
         $uploadedFile = null;
         if (null !== $request->file('receipt')) {
             $maxFileSize = env('MAX_INVOICE_FILE_SIZE', 16);
diff --git a/app/Domains/Invoice/Views/Partials/newInvoice/travel-expense-accounting.vue b/app/Domains/Invoice/Views/Partials/newInvoice/travel-expense-accounting.vue
index 1438c33..78b3029 100644
--- a/app/Domains/Invoice/Views/Partials/newInvoice/travel-expense-accounting.vue
+++ b/app/Domains/Invoice/Views/Partials/newInvoice/travel-expense-accounting.vue
@@ -41,10 +41,11 @@ const travelReasonComplete = computed(() =>
 /**
  * Wer gereist ist, steht später als Zahlungsgrund in der Belegliste, auf der EüR und auf dem Beleg. Wer
  * den Beleg einreicht, war meist selbst dabei -- deshalb der eigene Name als Vorschlag. Ohne Login
- * bleibt das Feld leer, und es hält den Ablauf auch dann nicht auf: Ein Name ist eine Hilfe, keine
- * Bedingung.
+ * bleibt das Feld leer; weiter geht es erst, wenn jemand eingetragen ist -- wie beim Reisegrund.
  */
 const travellers = ref(data.userName || '');
+
+const travellersComplete = computed(() => travellers.value.trim() !== '');
 const have_receipt = ref('')
 const amount = ref(0.00);
 const invoiceType = ref(null);
@@ -121,7 +122,7 @@ function handleFileChange(event) {
         />
     </fieldset><br /><br />
 
-  <fieldset v-if="travelReasonComplete">
+  <fieldset v-if="travelReasonComplete && travellersComplete">
     <legend><span style="font-weight: bolder;">Bist du mit dem ÖPNV gefahren oder besitzt du einen Beleg</span></legend>
     <input type="button" style="border-radius: 0; width: 100px;" @click="have_receipt='yes'" value="Ja" />
     <input type="button" style="border-radius: 0; width: 100px;" @click="getDistanceAllowance" value="Nein" />
@@ -129,7 +130,8 @@ function handleFileChange(event) {
 
   <br /><br />
 
-  <fieldset v-if="have_receipt === 'yes'">
+  <!-- Auch nach "Ja"/"Nein" gilt die Pflicht: Wer die Personen wieder löscht, kann nicht einreichen. -->
+  <fieldset v-if="travellersComplete && have_receipt === 'yes'">
     <legend><span style="font-weight: bolder;">Wie hoch ist der Betrag?</span></legend>
     <AmountInput v-model="amount" class="width-small" id="amount" name="amount"  /> Euro
 
@@ -161,7 +163,7 @@ function handleFileChange(event) {
     />
   </fieldset>
 
-  <fieldset v-else-if="distanceAllowance != null">
+  <fieldset v-else-if="travellersComplete && distanceAllowance != null">
     <legend><span style="font-weight: bolder;">Reiseinformationen</span></legend>
     Gesamtlänge des Reisewegs:
     <NumericInput
diff --git a/app/Models/CostUnit.php b/app/Models/CostUnit.php
index 8f82621..83beda2 100644
--- a/app/Models/CostUnit.php
+++ b/app/Models/CostUnit.php
@@ -11,7 +11,7 @@ use Illuminate\Database\Eloquent\Relations\HasOne;
 /**
  * @property string $name
  * @property string $type
- * @property string $billing_deadline
+ * @property string|null $billing_deadline Y-m-d, Abrechnungsschluss einschließlich des ganzen Tages
  * @property string $distance_allowance
  * @property boolean $mail_on_new
  * @property boolean $allow_new
diff --git a/app/Resources/CostUnitResource.php b/app/Resources/CostUnitResource.php
index 9dd570c..fe5af72 100644
--- a/app/Resources/CostUnitResource.php
+++ b/app/Resources/CostUnitResource.php
@@ -49,6 +49,7 @@ class CostUnitResource {
         $data = array_merge(
             $this->costUnit->toArray(),
             [
+                'billingDeadline' => $this->costUnit->billing_deadline,
                 'distanceAllowanceSmall' => new Amount($this->costUnit->distance_allowance, '')->toString(),
                 'distanceAllowanceFull' => new Amount($this->costUnit->distance_allowance, ' Euro')->toString(),
                 'totalAmount' => new Amount($totalAmount, ' Euro')->toString(),
diff --git a/app/Tasks/CloseCostUnit.php b/app/Tasks/CloseCostUnit.php
index 2e80dc3..2e55028 100644
--- a/app/Tasks/CloseCostUnit.php
+++ b/app/Tasks/CloseCostUnit.php
@@ -15,7 +15,6 @@ use Illuminate\Support\Facades\Mail;
 class CloseCostUnit implements CronTask {
     public function handle(): void
     {
-        $now = now();
         $costUnitRepository = new CostUnitRepository();
         $now = now();
         $billingResetEnd = clone $now;
@@ -25,7 +24,7 @@ class CloseCostUnit implements CronTask {
             $billingEnd = $costUnit['billing_deadline'];
 
             if ($billingEnd === null) {
-                $billingEnd = \DateTime::createFromFormat('Y-m-d H:i:s', $billingResetEnd)->format('Y-m-d H:i:s');
+                $billingEnd = $billingResetEnd->format('Y-m-d');
                 new ChangeCostUnitDetailsCommand(new ChangeCostUnitDetailsRequest(
                     CostUnit::where('id', $costUnit['id'])->first(),
                     Amount::fromString($costUnit['distance_allowance']),
@@ -34,9 +33,9 @@ class CloseCostUnit implements CronTask {
                 ))->execute();
             }
 
-            $billingEndTime = \DateTime::createFromFormat('Y-m-d H:i:s', $billingEnd);
+            $billingEndTime = \DateTime::createFromFormat('!Y-m-d', $billingEnd);
             if (false === $billingEndTime) {
-                $billingEndTime = \DateTime::createFromFormat('Y-m-d', $billingEnd);
+                $billingEndTime = \DateTime::createFromFormat('Y-m-d H:i:s', $billingEnd);
             }
 
             if (false === $billingEndTime) {
@@ -56,12 +55,10 @@ class CloseCostUnit implements CronTask {
 
                 continue;
             }
-            $billingEndTime->setTime(0,0,0);
-            $billingEndTime->add(new \DateInterval('P1D'));
+            // Der Abrechnungsschluss gilt einschließlich des ganzen Tages: bis 23:59:59 darf eingereicht werden.
+            $billingEndTime->setTime(23, 59, 59);
 
-
-
-            if ($billingEndTime < $now) {
+            if ($now > $billingEndTime) {
                 new ChangeCostUnitStateCommand(
                     new ChangeCostUnitStateRequest(
                         CostUnit::where('id', $costUnit['id'])->first(),false, false
diff --git a/database/migrations/2026_09_17_140010_change_billing_deadline_to_date_on_cost_units.php b/database/migrations/2026_09_17_140010_change_billing_deadline_to_date_on_cost_units.php
new file mode 100644
index 0000000..78a1f87
--- /dev/null
+++ b/database/migrations/2026_09_17_140010_change_billing_deadline_to_date_on_cost_units.php
@@ -0,0 +1,31 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * Der Abrechnungsschluss ist ein Tag, keine Uhrzeit: eingereicht werden darf bis einschließlich 23:59 des Stichtags.
+ * Die Uhrzeit, die bisher mitgespeichert wurde, hat der Cron ohnehin verworfen -- das Abschneiden ändert kein
+ * Verhalten. Erst normalisieren, dann den Typ ändern, damit das ALTER nichts abschneiden muss.
+ */
+return new class extends Migration {
+    public function up(): void
+    {
+        DB::table('cost_units')
+            ->whereNotNull('billing_deadline')
+            ->update(['billing_deadline' => DB::raw('DATE(billing_deadline)')]);
+
+        Schema::table('cost_units', function (Blueprint $table) {
+            $table->date('billing_deadline')->nullable()->change();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('cost_units', function (Blueprint $table) {
+            $table->dateTime('billing_deadline')->nullable()->change();
+        });
+    }
+};
diff --git a/tests/Feature/CostUnitBillingDeadlineTest.php b/tests/Feature/CostUnitBillingDeadlineTest.php
new file mode 100644
index 0000000..b4aa87b
--- /dev/null
+++ b/tests/Feature/CostUnitBillingDeadlineTest.php
@@ -0,0 +1,184 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Domains\CostUnit\Actions\ChangeCostUnitDetails\ChangeCostUnitDetailsCommand;
+use App\Domains\CostUnit\Actions\ChangeCostUnitDetails\ChangeCostUnitDetailsRequest;
+use App\Enumerations\CostUnitType;
+use App\Enumerations\UserRole;
+use App\Models\CostUnit;
+use App\Models\Tenant;
+use App\Models\User;
+use App\Tasks\CloseCostUnit;
+use App\ValueObjects\Amount;
+use DateTime;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCase;
+
+/**
+ * Der Abrechnungsschluss einer Kostenstelle.
+ *
+ * Er ist ein Tag, keine Uhrzeit: Abrechnungen dürfen bis einschließlich 23:59 des Stichtags eingereicht werden. Das
+ * Modal „Details anpassen" muss ihn anzeigen -- sonst löscht jedes Speichern den Wert unbemerkt.
+ */
+class CostUnitBillingDeadlineTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private Tenant $tenant;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->tenant = Tenant::create([
+            'slug' => 'wm',
+            'name' => 'Wilde Möhre',
+            'address_1' => 'Musterweg 1',
+            'email' => 't@example.com',
+            'email_finance' => 'finance@example.com',
+            'url' => parse_url(config('app.url'), PHP_URL_HOST),
+            'account_name' => 'Test e.V.',
+            'account_iban' => 'DE00',
+            'account_bic' => 'XY',
+            'city' => 'Stadt',
+            'postcode' => '00000',
+            'invoice_prefix' => 'WM',
+            'is_active_local_group' => true,
+            'has_active_instance' => true,
+        ]);
+
+        app()->instance('tenant', $this->tenant);
+
+        DB::table('cost_unit_types')->insert(['slug' => CostUnitType::COST_UNIT_TYPE_EVENT, 'name' => 'Veranstaltung']);
+
+        foreach ([UserRole::USER_ROLE_ADMIN, UserRole::USER_ROLE_GROUP_LEADER, UserRole::USER_ROLE_USER] as $role) {
+            UserRole::create(['slug' => $role, 'name' => $role]);
+        }
+    }
+
+    public function test_details_liefern_den_abrechnungsschluss_im_format_des_datumsfelds(): void
+    {
+        $costUnit = $this->makeCostUnit('2026-09-11');
+        $this->actingAs($this->makeAdmin());
+
+        $response = $this->getJson('/api/v1/cost-unit/' . $costUnit->id . '/details');
+
+        $response->assertOk();
+        $this->assertSame('2026-09-11', $response->json('costUnit.billingDeadline'));
+    }
+
+    public function test_details_ohne_abrechnungsschluss_liefern_null(): void
+    {
+        $costUnit = $this->makeCostUnit(null);
+        $this->actingAs($this->makeAdmin());
+
+        $response = $this->getJson('/api/v1/cost-unit/' . $costUnit->id . '/details');
+
+        $this->assertNull($response->json('costUnit.billingDeadline'));
+    }
+
+    public function test_speichern_uebernimmt_das_datum_aus_dem_formular(): void
+    {
+        $costUnit = $this->makeCostUnit('2026-09-11');
+        $this->actingAs($this->makeAdmin());
+
+        $this->postJson('/api/v1/cost-unit/' . $costUnit->id . '/details', ['formData' => [
+            'billingDeadline' => '2026-09-30',
+            'mailOnNew' => true,
+            'distanceAllowance' => '0,30',
+        ]])->assertOk()->assertJson(['status' => 'success']);
+
+        $this->assertSame('2026-09-30', $costUnit->fresh()->billing_deadline);
+    }
+
+    public function test_ein_geleertes_datumsfeld_entfernt_den_abrechnungsschluss_ohne_fehler(): void
+    {
+        $costUnit = $this->makeCostUnit('2026-09-11');
+        $this->actingAs($this->makeAdmin());
+
+        $this->postJson('/api/v1/cost-unit/' . $costUnit->id . '/details', ['formData' => [
+            'billingDeadline' => '',
+            'mailOnNew' => false,
+            'distanceAllowance' => '0,25',
+        ]])->assertOk()->assertJson(['status' => 'success']);
+
+        $this->assertNull($costUnit->fresh()->billing_deadline);
+    }
+
+    public function test_eine_uhrzeit_im_request_wird_nicht_gespeichert(): void
+    {
+        $costUnit = $this->makeCostUnit(null);
+
+        new ChangeCostUnitDetailsCommand(new ChangeCostUnitDetailsRequest(
+            $costUnit,
+            Amount::fromString('0,25'),
+            false,
+            new DateTime('2026-09-11 14:23:45'),
+        ))->execute();
+
+        $this->assertSame('2026-09-11', $costUnit->fresh()->billing_deadline);
+    }
+
+    public function test_am_stichtag_um_2359_ist_die_kostenstelle_noch_offen(): void
+    {
+        $costUnit = $this->makeCostUnit('2026-09-11');
+
+        $this->travelTo(new DateTime('2026-09-11 23:59:00'));
+        new CloseCostUnit()->handle();
+
+        $this->assertTrue((bool) $costUnit->fresh()->allow_new);
+    }
+
+    public function test_am_folgetag_schliesst_der_cron_die_kostenstelle(): void
+    {
+        $costUnit = $this->makeCostUnit('2026-09-11');
+
+        $this->travelTo(new DateTime('2026-09-12 00:05:00'));
+        new CloseCostUnit()->handle();
+
+        $this->assertFalse((bool) $costUnit->fresh()->allow_new);
+    }
+
+    public function test_ohne_abrechnungsschluss_setzt_der_cron_sechs_wochen_und_laesst_offen(): void
+    {
+        $costUnit = $this->makeCostUnit(null);
+
+        $this->travelTo(new DateTime('2026-09-12 00:05:00'));
+        new CloseCostUnit()->handle();
+
+        $costUnit = $costUnit->fresh();
+        $this->assertSame('2026-10-24', $costUnit->billing_deadline);
+        $this->assertTrue((bool) $costUnit->allow_new);
+    }
+
+    private function makeCostUnit(?string $billingDeadline): CostUnit
+    {
+        return CostUnit::create([
+            'tenant' => $this->tenant->slug,
+            'name' => 'Sommerlager',
+            'type' => CostUnitType::COST_UNIT_TYPE_EVENT,
+            'billing_deadline' => $billingDeadline,
+            'distance_allowance' => 0.25,
+            'mail_on_new' => false,
+            'allow_new' => true,
+            'archived' => false,
+        ]);
+    }
+
+    private function makeAdmin(): User
+    {
+        return User::create([
+            'username' => 'admin-' . uniqid() . '@example.com',
+            'email' => 'admin-' . uniqid() . '@example.com',
+            'firstname' => 'Test',
+            'lastname' => 'Person',
+            'password' => bcrypt('secret'),
+            'local_group' => $this->tenant->slug,
+            'user_role_main' => UserRole::USER_ROLE_USER,
+            'user_role_local_group' => UserRole::USER_ROLE_ADMIN,
+            'active' => true,
+        ]);
+    }
+}
diff --git a/tests/Feature/InvoicePurposeTest.php b/tests/Feature/InvoicePurposeTest.php
index 402b4ae..6c0b0b9 100644
--- a/tests/Feature/InvoicePurposeTest.php
+++ b/tests/Feature/InvoicePurposeTest.php
@@ -183,12 +183,47 @@ class InvoicePurposeTest extends TestCase
 
     public function test_travel_costs_without_travellers_record_only_the_reason(): void
     {
-        // Ohne Login steht im Formular niemand drin -- das darf den Beleg nicht aufhalten.
+        // Der Command selbst verlangt keine Personen: Abrechnungskorrekturen laufen ohne sie durch. Die
+        // Pflicht beim Einreichen prüft der SaveInvoiceController -- siehe die Tests unten.
         $invoice = $this->submit(InvoiceType::INVOICE_TYPE_TRAVELLING, travelReason: 'Landeslager');
 
         $this->assertSame('Landeslager', $invoice->purpose);
     }
 
+    /**
+     * Eine Fahrtkostenabrechnung über das Formular, als Kilometerpauschale ohne Beleg.
+     */
+    private function postTravelExpense(CostUnit $costUnit, ?string $travellers): \Illuminate\Testing\TestResponse
+    {
+        return $this->postJson('/api/v1/invoice/new/' . $costUnit->id . '/' . InvoiceType::INVOICE_TYPE_TRAVELLING, [
+            'name' => 'Max Mustermann',
+            'amount' => '100',
+            'otherText' => 'Halle – Leipzig',
+            'decision' => 'payout',
+            'travelReason' => 'Landeslager',
+            'travellers' => $travellers,
+        ]);
+    }
+
+    public function test_submitting_travel_costs_requires_who_travelled(): void
+    {
+        $costUnit = $this->makeCostUnit();
+
+        foreach ([null, '', '   '] as $travellers) {
+            $this->postTravelExpense($costUnit, $travellers)
+                ->assertJson(['status' => 'error', 'message' => 'Bitte gib an, welche Personen gereist sind.']);
+        }
+
+        $this->assertSame(0, Invoice::count());
+    }
+
+    public function test_submitting_travel_costs_with_travellers_is_accepted(): void
+    {
+        $this->postTravelExpense($this->makeCostUnit(), 'Mika und Kim')->assertJson(['status' => 'success']);
+
+        $this->assertSame('Landeslager — Mika und Kim', Invoice::sole()->purpose);
+    }
+
     public function test_a_refund_records_no_purpose(): void
     {
         // Beitragserstattungen entstehen ohne Freitext. `null` statt Leerstring: So greift für sie