const options = {
  method: 'POST',
  headers: {'x-organization-id': '<x-organization-id>', 'Content-Type': 'application/json'},
  body: JSON.stringify({mapping: {}})
};

fetch('https://api.dcycle.io/v2/imports/{import_id}/mapping', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "import_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "mapping": {}
}