const options = {method: 'GET', headers: {Authorization: 'Bearer <token>'}};

fetch('https://api.gnosispay.com/api/v1/owners/add/transaction-data', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "data": {
    "domain": {
      "verifyingContract": "0x3270bf32AB647e90eF94A026c70Aa1daaaDA2382",
      "chainId": 100
    },
    "primaryType": "ModuleTx",
    "types": {
      "ModuleTx": [
        {
          "type": "bytes",
          "name": "data"
        }
      ]
    },
    "message": {
      "data": "0xa9059cbb0000000000000000000000003270bf32ab647e90ef94a026c70aa1daaaada2382",
      "salt": "0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef"
    }
  }
}