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

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

{
  "import_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "total_rows": 123,
  "valid_rows": 123,
  "error_rows": 123,
  "page": 123,
  "page_size": 123,
  "total_pages": 123,
  "errors_by_column": {},
  "rows": [
    {
      "row_index": 123,
      "data": {},
      "errors": {}
    }
  ]
}