diff --git a/app/Invoice/Contracts/InvoiceCreator.php b/app/Invoice/Contracts/InvoiceCreator.php
new file mode 100644
index 00000000..363d239b
--- /dev/null
+++ b/app/Invoice/Contracts/InvoiceCreator.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Invoice\Creators;
+
+use App\Invoice\BillKind;
+use App\Invoice\Data\PositionData;
+use App\Invoice\Data\ReceiverData;
+use Illuminate\Support\Collection;
+
+interface InvoiceCreator {
+
+    public function getVia(): BillKind;
+
+    public function getUsage(): string;
+
+    /** @return Collection<int, PositionData> */
+    public function getPositions(): Collection;
+
+    public function getReceiver(): ReceiverData;
+
+}
diff --git a/app/Invoice/Models/Invoice.php b/app/Invoice/Models/Invoice.php
index c3f49c15..ebd62cac 100644
--- a/app/Invoice/Models/Invoice.php
+++ b/app/Invoice/Models/Invoice.php
@@ -4,12 +4,12 @@ namespace App\Invoice\Models;
 
 use App\Invoice\BillDocument;
 use App\Invoice\BillKind;
+use App\Invoice\Creators\InvoiceCreator;
 use App\Invoice\Data\ReceiverData;
 use App\Invoice\Enums\InvoiceStatus;
 use App\Invoice\InvoiceDocument;
 use App\Invoice\InvoiceSettings;
 use App\Invoice\RememberDocument;
-use App\Member\Factories\MemberInvoiceFactory;
 use Database\Factories\Invoice\Models\InvoiceFactory;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
@@ -41,10 +41,7 @@ class Invoice extends Model
         return $this->hasMany(InvoicePosition::class);
     }
 
-    /**
-     * @param Collection<int, Member> $members
-     */
-    public static function createFromFactory(MemberInvoiceFactory $factory): self
+    public static function createFromFactory(InvoiceCreator $factory): self
     {
         $invoice = new self([
             'to' => $factory->getReceiver(),
diff --git a/app/Member/Factories/MemberInvoiceFactory.php b/app/Member/Factories/MemberInvoiceFactory.php
index 6c773866..3f749f6e 100644
--- a/app/Member/Factories/MemberInvoiceFactory.php
+++ b/app/Member/Factories/MemberInvoiceFactory.php
@@ -3,13 +3,14 @@
 namespace App\Member\Factories;
 
 use App\Invoice\BillKind;
+use App\Invoice\Creators\InvoiceCreator;
 use App\Invoice\Data\PositionData;
 use App\Invoice\Data\ReceiverData;
 use App\Member\Member;
 use App\Payment\Subscription;
 use Illuminate\Support\Collection;
 
-class MemberInvoiceFactory
+class MemberInvoiceFactory implements InvoiceCreator
 {
 
     /** @var Collection<int, Member> */
@@ -71,8 +72,7 @@ class MemberInvoiceFactory
         return 'Mitgliedsbeitrag für ' . $this->member->lastname;
     }
 
-    /** @return Collection<int, PositionData> */
-    public function getPositions() {
+    public function getPositions(): Collection {
         /** @var Collection<int, PositionData> */
         $positions = collect([]);
         foreach ($this->positions as $member) {
@@ -81,6 +81,7 @@ class MemberInvoiceFactory
                 $positions->push(PositionData::from([
                     'description' => str($child->name)->replace('{name}', $member->firstname . ' ' . $member->lastname)->replace('{year}', (string) $this->year),
                     'price' => $child->amount,
+                    /** @todo check if this is correct */
                     'member_id' => $member->id,
                     'id' => null,
                 ]));