Worker is not producing messages for queue

// src/routes/mail.ts
export async function handleRequest(
    request: Request,
    env: Env,
): Promise<Response | null> {
    if (request.method === "PATCH") {
        (...)

        console.log("Verification code", code);

        try {
            env.MAIL_QUEUE.send({
                type: "mail_verification",
                code: code.toString(),
            });
        } catch (err) {
            console.error(err);

            return new Response(
                JSON.stringify({ success: false, mailQueued: false }),
                { status: 202 },
            );
        }

        return new Response(JSON.stringify({ success: true }), { status: 200 });
    }

    return notFound();
}

$ wrangler queues info mail-queue
(...)
Number of Producers: 1
(...)