const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"mailing_list":1,"email":"[email protected]"}'
};

fetch('https://api.thanks.io/api/v2/recipients', options)
  .then(response => response.json())
  .then(response => console.log(response))
  .catch(err => console.error(err));

{
  "province": "NY",
  "city": "Warwick",
  "name": "Example Name",
  "company": "",
  "dob": "",
  "country": "US",
  "address": "1 Test Street",
  "address2": "",
  "email": "[email protected]",
  "phone": "",
  "custom1": null,
  "custom2": null,
  "custom3": null,
  "custom4": null,
  "postal_code": "10990",
  "id": 18092812,
  "mailing_list_id": 1
}