const options = {method: 'GET', headers: {Authorization: 'Bearer <token>'}};

fetch('https://api.valox.co/api/v1/ibans/available', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "data": {
    "available": true
  }
}