diff --git a/app/Filament/Resources/RequestCharacteristicResource.php b/app/Filament/Resources/RequestCharacteristicResource.php
index f76f84b..93c9695 100644
--- a/app/Filament/Resources/RequestCharacteristicResource.php
+++ b/app/Filament/Resources/RequestCharacteristicResource.php
@@ -256,8 +256,12 @@ class RequestCharacteristicResource extends Resource
                             ->label('Serial Number')
                             ->reactive()
                             ->minLength(13)
-                            ->readOnly(fn (callable $get) => (! $get('aufnr')))
-                            ->afterStateUpdated(function (callable $set) {
+                            ->readOnly(fn (callable $get) => (! $get('aufnr') || $get('approver_type') != 'Stop'))
+                            ->afterStateUpdated(function ($state, callable $set, callable $get) {
+                                $appTyp = $get('approver_type');
+                                if ($appTyp != 'Stop') {
+                                    $set('gernr', null);
+                                }
                                 $set('updated_by', Filament::auth()->user()?->name);
                             })
                             // ->rules([