const options = {method: 'POST', headers: {cookie: 'session='}};

fetch('https://api.example.com/v1/regions/global/notifications/inbox/read-all', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "success": true,
  "data": {
    "markedCount": 123
  },
  "meta": {}
}