$Payment = $this->paymentRepository->findOneBy(['method_class' => Conveni::class]);

                // この部分を追加
                //  ----------------------------------
                if ($Payment === null) {
                    $Payment->remove('convenience');
                }
                // ----------------------------------

                $data = $event->getData();
                $form = $event->getForm();
                // 支払い方法が一致しなければremove
                if ($Payment->getId() != $data['Payment']) {
                    $form->remove('convenience');
                }