const url = 'https://api.thanks.io/api/v2/recipients-utils/create-multiple';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '[{"mailing_list":1,"name":"Tobias First","address":"987 Main Street","address2":null,"city":"LENEXA","province":"KS","postal_code":"66216","country":"US","dob":"04/23/1981","custom1":null,"custom2":null,"email":"[email protected]","phone":"1234567890"},{"mailing_list":1,"email":"[email protected]","phone":"1234567890"}]'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}

[
  {
    "province": "KS",
    "city": "Lenexa",
    "name": "Tobias First",
    "company": null,
    "dob": "04/23/1981",
    "country": "US",
    "address": "987 Main Street",
    "address2": "",
    "email": "[email protected]",
    "phone": "1234567890",
    "custom1": null,
    "custom2": null,
    "postal_code": "66216"
  },
  {
    "province": "KS",
    "city": "Lenexa",
    "name": "Tobias Second",
    "company": null,
    "dob": "04/23/1981",
    "country": "US",
    "address": "654 Main Street",
    "address2": "",
    "email": "[email protected]",
    "phone": "1234567890",
    "custom1": null,
    "custom2": null,
    "postal_code": "66216",
    "error": "This address is already on this mailing list."
  }
]