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);

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

        $to = $data->isTest ? $kirby->users() : page("inscription")->subscribers()->toStructure()->pluck("email", true, true);
        $subject = $data->isTest ? "[TEST] - " . (string) $emailPage->title() : (string) $emailPage->title();
        
        try {
            if ($kirby->email([
                'from'    => "info@actuel-inactuel.fr",
                'to'      => $to,
                'cc'      => 'contact@adrien-payet.fr',
                'subject' => $subject,
                'template' => 'newsletter',
                'data'    => [
                    "body" => $emailPage->body()
                ]
            ])->isSent()) {
                $emailPage->changeStatus("listed");
                return json_encode([
                    'status' => 'success', 
                    'message' => 
                    'Email envoyé avec succès.'
                ]);
            } else {
                return json_encode([
                    "status" => "error",
                    "message" => "Erreur lors de l'envoi de l'email.",
                ]);
            }
        } catch (Exception $error) {
            return json_encode(['status' => 'error', 'message' => $error->getMessage()]);
        }
    }
];