curl --request POST \
  --url https://gobl.dev/v0/sign \
  --header 'Content-Type: application/json' \
  --data '
{
  "data": "<unknown>",
  "template": "<unknown>",
  "privatekey": {
    "kty": "EC",
    "crv": "P-256",
    "alg": "ES256",
    "use": "sig",
    "kid": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "x": "<string>",
    "y": "<string>",
    "d": "<string>"
  },
  "type": "<string>",
  "envelop": true
}
'

{
  "code": 422,
  "key": "<string>",
  "message": "<string>",
  "faults": [
    {
      "properties": [
        "<string>"
      ],
      "description": "<string>"
    }
  ]
}