问如何解决这个错误“SyntaxError:意外的token < in JSON at position 0”

EN

  var d={
  "cand_name": "markzuck",
  "candidate_management_cand_info__pkey": 14,
  "candidate_management_job_id__fkey": "1",
  "cand_email": "jagadeesh.korikana@gmail.com",
  "cand_altemail": "b@gmail.com",
  "cand_contact": "6576575576",
  }; 

  var url =  fetch(url, {
    method: 'POST',
    body: JSON.stringify(d),
    headers: {'Content-Type': 'application/json'}
    }).then(response => { 
       alert(JSON.stringify(d));
       return response.json(); 
    }).then(data => { 
       alert(JSON.stringify(data));
    }).catch(err => {
       console.log(d);
       alert(err);
   });