curl --request POST \
  --url https://restapi.sign.plus/v2/envelope/{envelope_id}/signing_steps \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "signing_steps": [
    {
      "recipients": [
        {
          "name": "<string>",
          "email": "<string>",
          "role": "SIGNER",
          "id": "<string>",
          "uid": "<string>",
          "verification": {
            "type": "SMS",
            "value": "<string>"
          }
        }
      ]
    }
  ]
}
'

{
  "id": "<string>",
  "name": "<string>",
  "comment": "<string>",
  "pages": 123,
  "flow_type": "REQUEST_SIGNATURE",
  "legality_level": "SES",
  "status": "DRAFT",
  "created_at": 123,
  "updated_at": 123,
  "expires_at": 123,
  "num_recipients": 123,
  "is_duplicable": true,
  "signing_steps": [
    {
      "recipients": [
        {
          "name": "<string>",
          "email": "<string>",
          "role": "SIGNER",
          "id": "<string>",
          "uid": "<string>",
          "verification": {
            "type": "SMS",
            "value": "<string>"
          }
        }
      ]
    }
  ],
  "documents": [
    {
      "id": "<string>",
      "name": "<string>",
      "filename": "<string>",
      "page_count": 123,
      "pages": [
        {
          "width": 123,
          "height": 123
        }
      ]
    }
  ],
  "notification": {
    "subject": "<string>",
    "message": "<string>",
    "reminder_interval": 123
  },
  "attachments": {
    "settings": {
      "visible_to_recipients": true
    },
    "recipients": [
      {
        "recipient_id": "<string>",
        "recipient_name": "<string>",
        "placeholders": [
          {
            "recipient_id": "<string>",
            "id": "<string>",
            "name": "<string>",
            "hint": "<string>",
            "required": true,
            "multiple": true,
            "files": [
              {
                "id": "<string>",
                "name": "<string>",
                "size": 123,
                "mimetype": "<string>"
              }
            ]
          }
        ]
      }
    ]
  }
}