Method: externaltransactions.getexternaltransaction

```
curl \
  -X GET \
  'https://androidpublisher.googleapis.com/androidpublisher/v3/applications/com.example.app/externalTransactions/1234567890' \
  -H 'Accept: application/json' \
  -H 'Authorization: Bearer [YOUR_ACCESS_TOKEN]'
```

{
  "createTime": "2023-04-06T13:48:11.694Z",
  "currentPreTaxAmount": {
    "currency": "USD",
    "priceMicros": "12000000"
  },
  "currentTaxAmount": {
    "currency": "USD",
    "priceMicros": "1200000"
  },
  "externalTransactionId": "ext-trans-id-123",
  "oneTimeTransaction": {
    "externalTransactionToken": "one-time-token-456"
  },
  "originalPreTaxAmount": {
    "currency": "USD",
    "priceMicros": "15000000"
  },
  "originalTaxAmount": {
    "currency": "USD",
    "priceMicros": "1500000"
  },
  "packageName": "com.example.app",
  "recurringTransaction": {
    "externalSubscription": {
      "subscriptionType": "RECURRING"
    },
    "externalTransactionToken": "recurring-token-789",
    "initialExternalTransactionId": "ext-trans-id-001",
    "otherRecurringProduct": {}
  },
  "testPurchase": {},
  "transactionProgramCode": 11,
  "transactionState": "TRANSACTION_REPORTED",
  "transactionTime": "2023-04-06T14:00:00.000Z",
  "userTaxAddress": {
    "regionCode": "US"
  }
}