OAuth 2.0

https://app.brevo.com/oauth/authorize?
  response_type=code&
  client_id=YOUR_CLIENT_ID&
  redirect_uri=YOUR_REDIRECT_URI&
  scope=email%20contacts&
  state=random_string

const response = await fetch('https://api.brevo.com/v3/account', {
  headers: {
    'Authorization': 'Bearer YOUR_ACCESS_TOKEN',
    'Accept': 'application/json'
  }
});

const refreshToken = async () => {
  const response = await fetch('https://api.brevo.com/v3/oauth/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'refresh_token',
      refresh_token: 'YOUR_REFRESH_TOKEN',
      client_id: 'YOUR_CLIENT_ID',
      client_secret: 'YOUR_CLIENT_SECRET'
    })
  });
  return response.json();
};