const issuances = students.map((student, index) => ({
  institution_uuid: INSTITUTION_UUID,
  course_uuid: COURSE_UUID,
  student_uuid: student.uuid,
  file_uuid: files[index].uuid,
  status: 'issued',
  issued_at: new Date().toISOString(),
}));

const results = await Promise.all(
  issuances.map(payload =>
    fetch('https://api.dokstamp.com/certificates', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${TOKEN}`,
        'Accept': 'application/json',
        'Content-Type': 'application/json',
        'X-Tenant': TENANT,
      },
      body: JSON.stringify(payload),
    }).then(r => r.json())
  )
);

const verificationUrls = results.map(r => r.data.public_verification_url);

use GuzzleHttp\Client;
use GuzzleHttp\Pool;
use GuzzleHttp\Psr7\Request;

$client = new Client(['base_uri' => 'https://api.dokstamp.com']);
$headers = [
    'Authorization' => "Bearer $token",
    'Accept'        => 'application/json',
    'Content-Type'  => 'application/json',
    'X-Tenant'      => $tenant,
];

$requests = function () use ($students, $files, $headers) {
    foreach ($students as $i => $student) {
        $body = json_encode([
            'institution_uuid' => INSTITUTION_UUID,
            'course_uuid'      => COURSE_UUID,
            'student_uuid'     => $student['uuid'],
            'file_uuid'        => $files[$i]['uuid'],
            'status'           => 'issued',
            'issued_at'        => now()->toIso8601String(),
        ]);
        yield new Request('POST', 'certificates', $headers, $body);
    }
};

$pool = new Pool($client, $requests(), ['concurrency' => 10]);
$pool->promise()->wait();