Added admin action to make an expired order pending again

src/pretix/control/forms/orders.py

@@ -1,6 +1,7 @@
 from django import forms
 from django.core.exceptions import ValidationError
 from django.db import models
+from django.utils.timezone import now
 from django.utils.translation import ugettext_lazy as _
 
 from pretix.base.forms import I18nModelForm
@@ -15,6 +16,12 @@ class ExtendForm(I18nModelForm):
             'expires': forms.DateTimeInput(attrs={'class': 'datetimepicker'}),
         }
 
+    def clean(self):
+        data = super().clean()
+        if data['expires'] < now():
+            raise ValidationError(_('The new expiry date needs to be in the future.'))
+        return data
+
 
 class ExporterForm(forms.Form):