Get transaction for a gateway transaction ID

{
  "agreement_payment_type": "recurring",
  "amount": 1000,
  "authorisation_mode": "web",
  "authorisation_summary": {
    "three_d_secure": {
      "required": true,
      "version": "2.1.0"
    }
  },
  "card_details": {
    "billing_address": {
      "city": "London",
      "country": "GB",
      "county": "county",
      "line1": "address line 1",
      "line2": "address line 2",
      "postcode": "Ex 8RR"
    },
    "card_brand": "Visa",
    "card_type": "credit",
    "cardholder_name": "J Doe",
    "expiry_date": "11/43",
    "first_digits_card_number": "424242",
    "last_digits_card_number": "4242"
  },
  "credential_external_id": "7a7a718cb8b0401f8b8f4cdda9804073",
  "description": "New passport application",
  "email": "citizen@example.org",
  "exemption": {
    "outcome": {
      "result": "honoured"
    },
    "requested": true,
    "type": "corporate"
  },
  "fee": 2,
  "gateway_account_id": "1",
  "gateway_payout_id": "po_mdoiu23jkdj1kj23sd",
  "gateway_transaction_id": "fd21-1mdknkls1-2121-csdf",
  "language": "en",
  "net_amount": -2,
  "parent_transaction_id": "4dfdhapsdgftgkpp029d5kdfau5f",
  "payment_provider": "sandbox",
  "reason": "fraudulent",
  "reference": "payment reference",
  "refund_summary": {
    "status": "unavailable"
  },
  "refunded_by": "dj8923eihsdih23hkjfe8d",
  "refunded_by_user_email": "test@example.org",
  "return_url": "https://service-name.gov.uk/transactions/12345",
  "service_id": "baea0585e30d4acbb438524fca82b51e",
  "settlement_summary": {
    "settled_date": "2022-01-26"
  },
  "source": "CARD_API",
  "state": {
    "can_retry": true,
    "code": "P0030",
    "finished": true,
    "message": "Payment was cancelled by the user",
    "status": "cancelled"
  },
  "total_amount": 1000,
  "transaction_id": "9np5pocnotgkpp029d5kdfau5f",
  "transaction_type": "PAYMENT",
  "wallet_type": "APPLE_PAY"
}