install:

yarn add @workchain/postal-code

add to api schema.json:

{
  "attributes": {
    "postalCode": {
      "type": "customField",
      "customField": "plugin::postal-code.postal",
      "maxLength": 8,
      "regex": "^\\d{3}-?\\d{4}$",
      "required": true,
    },
    "prefecture": {
      "type": "customField",
      "customField": "plugin::postal-code.prefecture",
      "maxLength": 40,
      "required": true,
    },
    "address1": {
      "type": "string",
      "maxLength": 40,
    },
  },
}