curl --request POST \
  --url https://api.getsly.ai/v1/v1/ucp/checkouts/{id}/instruments \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "type": "card",
  "processor": "<string>",
  "processor_token": "<string>",
  "last_four": "<string>"
}
'

{
  "data": {
    "id": "<string>",
    "type": "card",
    "processor": "<string>",
    "processor_token": "<string>",
    "last_four": "<string>"
  }
}