actuel-inactuel/site/config/routes/send-newsletter.php

<?php

return [
    'pattern' => '/send-newsletter.json',
    'method' => 'POST',
    'action' => function () {
        $jsonRequest = file_get_contents("php://input");
        $data = json_decode($jsonRequest);

        if (!$data || !isset($data->pageUri) || !isset($data->isTest)) {
            return json_encode([
                'status' => 'error',
                'message' => 'Invalid request data. Required fields: pageUri, isTest.'
            ]);
        }

        $kirby = kirby();
        $emailPage = page('inscription')->childrenAndDrafts()->find($data->pageUri);

        if (!$emailPage) {
            return json_encode([
                'status' => 'error',
                'message' => 'The specified page does not exist.'
            ]);
        }

        $recipients = $data->isTest
            ? $kirby->users()->pluck('email', null, true)
            : page('inscription')->subscribers()->toStructure()->pluck('email', true, true);

        if (empty($recipients)) {
            return json_encode([
                'status' => 'error',
                'message' => 'No recipients found.'
            ]);
        }

        $subject = $data->isTest
            ? "[TEST] - " . $emailPage->title()->value()
            : $emailPage->title()->value();

        $from = new \Kirby\Cms\User([
            'email' => 'info@actuel-inactuel.fr',
            'name'  => 'actuel-inactuel',
          ]);
        
        try {
            foreach ($recipients as $recipient) {
                $kirby->email([
                    'from' => $from,
                    'to' => $recipient,
                    'subject' => $subject,
                    'template' => 'newsletter',
                    'data' => [
                        'body' => $emailPage->body()
                    ]
                ]);
            }

            if (!$data->isTest) {
                $emailPage->changeStatus('listed');
            }

            return json_encode([
                'status' => 'success',
                'message' => 'Email(s) sent successfully.'
            ]);
        } catch (Exception $error) {
            return json_encode([
                'status' => 'error',
                'message' => $error->getMessage() . " file " . $error->getFile() . " line " . $error->getLine()
            ]);
        }
    }
];