const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"to_name":"Sample Recipient","to_address":"1 Main Street","to_address2":"Apartment 1","to_city":"Woodbridge","to_state":"NJ","to_postal_code":"07095","to_country":"US","return_name":"6x9 Sample Business Name","front_image_url":"https://s3.amazonaws.com/cdn.thanks.io/user_image_library/1533645579.png","message":"This is an example test postcard message.","handwriting_style":"5","handwriting_color":"back","custom_background_image":"https://s3.amazonaws.com/content.thanks.io/templates/images/c09d39aadfc-3701d4467b8/3c375a60-6de5-11ee-9ea8-7374ba13eca7.png","qrcode_url":"https://www.google.com","size":"6x9"}'
};

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

{
  "proof_url": "https://s3.amazonaws.com/content.thanks.io/sls-order-proofs/pdfs/b048b2f4-6c0c-7240-e4d1-1211f2619388.pdf"
}