Send emails with PHP

<?php

const FLARESEND_URL = 'https://mailer.example.com';

final class FlaresendError extends RuntimeException
{
    public function __construct(
        public readonly int $status,
        public readonly string $type,
        public readonly string $errorCode,
        string $message,
        public readonly ?string $param = null,
    ) {
        parent::__construct($message);
    }
}

function flaresend_send(array $email, ?string $idempotencyKey = null): array
{
    $headers = [
        'Authorization: Bearer ' . getenv('FLARESEND_API_KEY'),
        'Content-Type: application/json',
    ];
    if ($idempotencyKey !== null) {
        $headers[] = 'Idempotency-Key: ' . $idempotencyKey;
    }

    $ch = curl_init(FLARESEND_URL . '/v1/emails');
    curl_setopt_array($ch, [
        CURLOPT_POST => true,
        CURLOPT_HTTPHEADER => $headers,
        CURLOPT_POSTFIELDS => json_encode($email, JSON_THROW_ON_ERROR),
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_TIMEOUT => 30,
    ]);
    $body = curl_exec($ch);
    if ($body === false) {
        throw new RuntimeException('network error: ' . curl_error($ch));
    }
    $status = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
    curl_close($ch);

    $json = json_decode($body, true);
    if ($status >= 300) {
        $e = $json['error'] ?? ['type' => 'internal_error', 'code' => "http_$status", 'message' => substr($body, 0, 200)];
        throw new FlaresendError($status, $e['type'], $e['code'], $e['message'], $e['param'] ?? null);
    }
    return $json;
}

$result = flaresend_send([
    'from' => 'Acme <hello@acme.com>',
    'to' => 'ada@example.com',
    'subject' => 'Hello from PHP',
    'html' => '<p>It works.</p>',
    'text' => 'It works.',
], 'hello-php-1');

echo $result['id'], ' ', $result['status'], PHP_EOL; // email_01K6B2Y4ZP9R3M7T8V5N2QXW4C queued

{
  "error": {
    "type": "validation_error",
    "code": "invalid_body",
    "message": "subject is required",
    "param": "subject"
  }
}

try {
    flaresend_send($email, "welcome-$userId");
} catch (FlaresendError $e) {
    error_log("$e->status $e->errorCode: {$e->getMessage()}");
}

$email['attachments'] = [[
    'filename' => 'invoice.pdf',
    'content' => base64_encode(file_get_contents('invoice.pdf')),
    'type' => 'application/pdf',
]];