const options = {method: 'GET'};

fetch('https://api.gnosispay.com/api/v1/webhooks/message/{partnerId}', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "message": "<string>",
  "nonce": "<string>"
}