{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "invoice",
  "type": "object",
  "required": [
    "invoice_id",
    "total"
  ],
  "properties": {
    "invoice_id": {
      "type": "string"
    },
    "total": {
      "type": "number",
      "minimum": 0
    },
    "currency": {
      "type": "string",
      "pattern": "^[A-Z]{3}$"
    }
  }
}