fixed from error

include/membership.php

@@ -124,6 +124,7 @@ class Membership extends Renderer {
                 $message .= $field . ': ' . $value . "\n";
             }
             $attachment = [
+                'Mitgliedsantrag.pdf' => ['content' => $this->createPdf($formData), 'type' => 'application/pdf']
             ];
             $this->sendMail($mail, 'Mitgliedsantrag', $message, '', $attachment);
             $this->templateName = 'membership_success';