curl --request GET \
  --url {schemes}://api.upsun.com/organizations/{organization_id}/prepayment \
  --header 'Authorization: Bearer <token>'

{
  "prepayment": {
    "prepayment": {
      "organization_id": "<string>",
      "balance": {
        "formatted": "<string>",
        "amount": 123,
        "currency_code": "<string>",
        "currency_symbol": "<string>"
      },
      "last_updated_at": "<string>",
      "sufficient": true,
      "fallback": "<string>"
    }
  },
  "_links": {
    "self": {
      "href": "<string>"
    },
    "transactions": {
      "href": "<string>"
    }
  }
}