> ## Documentation Index
> Fetch the complete documentation index at: https://docs.blnkfinance.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Transaction hooks
> Register PRE_TRANSACTION and POST_TRANSACTION hooks with the Hooks API, handle deliveries, and configure retries.
export const CtaCallout = props => {
const {title, buttonLabel, href, trackingEvent, buttonTarget, rel = "noopener noreferrer", children} = props;
const handleCtaClick = () => {
if (typeof window === "undefined" || !trackingEvent) {
return;
}
try {
window.dispatchEvent(new CustomEvent("blnk:docs-cta", {
detail: {
name: trackingEvent,
href
}
}));
} catch {}
try {
window.posthog?.capture?.(trackingEvent, {
href
});
} catch {}
const gaPayload = {
cta_href: href
};
try {
window.gtag?.("event", trackingEvent, gaPayload);
} catch {}
try {
window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
event: trackingEvent,
...gaPayload
});
} catch {}
};
const isExternal = typeof href === "string" && (/^https?:\/\//i).test(href);
const target = buttonTarget ?? (isExternal ? "_blank" : undefined);
const linkRel = isExternal ? rel : undefined;
return ;
};
Available in version 0.8.4 and later.
Transaction hooks let you plug custom logic into your transaction lifecycle, before or after a transaction is processed, without changing how Blnk records the ledger entry.
Register an endpoint for each stage you care about, and Blnk calls it with the transaction context so you can validate, enrich, or trigger side effects at the right moment.
**Note:** Blnk only sends `transaction.*` events to transaction hooks. Other events are not supported. See [Supported events](/webhooks/events) for the full list of transaction event names.
***
## Hook types
Blnk supports two hook types:
* `PRE_TRANSACTION`: before a transaction is applied
* `POST_TRANSACTION`: after a transaction is applied
`PRE_TRANSACTION` runs before a transaction is applied.
Use it for validation, fraud checks, or enriching transaction data while the transaction is still in an early state, for example `QUEUED`.
```json PRE_TRANSACTION payload wrap expandable {3} theme={"system"}
{
"event": "transaction.applied",
"hook_type": "PRE_TRANSACTION",
"data": {
"precise_amount": 20000,
"amount": 200,
"precision": 100,
"transaction_id": "txn_9c2f1a8e-4b3d-4c91-9f2a-1a7b6c5d4e3f",
"parent_transaction": "",
"source": "bln_7f91a1ae-6073-4b7a-952c-23abf94a6634",
"destination": "bln_59b83b9c-842c-427f-91eb-43cdeaf5c01a",
"reference": "INV-2025-0008912",
"currency": "GBP",
"description": "Wallet top-up",
"status": "QUEUED",
"hash": "623e05ceb7ca7b02a9318092de7b75d8c668628e2db76c42b621b61055b10b3e",
"allow_overdraft": true,
"inflight": false,
"skip_queue": false,
"created_at": "2025-02-23T09:43:49.623494+01:00",
"scheduled_for": "0001-01-01T00:00:00Z",
"inflight_expiry_date": "0001-01-01T00:00:00Z"
}
}
```
`POST_TRANSACTION` runs after a transaction is applied.
Use it for notifications, workflow updates, or forwarding data to external systems once the transaction has been processed.
```json POST_TRANSACTION payload wrap expandable {3} theme={"system"}
{
"event": "transaction.applied",
"hook_type": "POST_TRANSACTION",
"data": {
"precise_amount": 20000,
"amount": 200,
"precision": 100,
"transaction_id": "txn_9c2f1a8e-4b3d-4c91-9f2a-1a7b6c5d4e3f",
"parent_transaction": "",
"source": "bln_7f91a1ae-6073-4b7a-952c-23abf94a6634",
"destination": "bln_59b83b9c-842c-427f-91eb-43cdeaf5c01a",
"reference": "INV-2025-0008912",
"currency": "GBP",
"description": "Wallet top-up",
"status": "APPLIED",
"hash": "623e05ceb7ca7b02a9318092de7b75d8c668628e2db76c42b621b61055b10b3e",
"allow_overdraft": true,
"inflight": false,
"skip_queue": false,
"created_at": "2025-02-23T09:43:49.623494+01:00",
"scheduled_for": "0001-01-01T00:00:00Z",
"inflight_expiry_date": "0001-01-01T00:00:00Z"
}
}
```
Treat `data` as the contract for your integration; fields depend on the transaction type and Blnk version. Always handle unknown keys safely when parsing JSON.
***
## Getting started
Register your webhook URL with the [Hooks API](/reference/create-hooks):
Only the [master key](/advanced/secure-blnk#master-key) can create, update, view, list, or delete hooks. Regular API keys cannot, even if they include `hooks` scopes.
```bash cURL wrap theme={"system"}
curl -X POST "http://YOUR_BLNK_INSTANCE_URL/hooks" \
-H "X-Blnk-Key: YOUR_MASTER_KEY" \
-H "Content-Type: application/json" \
-d '{
"name": "Pre-transaction validation",
"url": "https://api.example.com/blnk/hooks/pre",
"type": "PRE_TRANSACTION",
"active": true,
"timeout": 30,
"retry_count": 3
}'
```
| Field | Description |
| :------------ | :--------------------------------------------------------------------------- |
| `name` | Human-readable label for operators and logs. |
| `url` | Absolute `HTTPS` or `HTTP` URL that accepts requests from Blnk. |
| `type` | Either `PRE_TRANSACTION` or `POST_TRANSACTION`. |
| `active` | When `false`, Blnk skips this hook until you enable it again. |
| `timeout` | Maximum time in seconds Blnk waits for your endpoint to respond per attempt. |
| `retry_count` | Maximum additional attempts after a failed delivery. |
```json 201 Created wrap theme={"system"}
{
"hook_id": "hoo_2vN9KxQpA1wM4rL6yB8cD0eF",
"name": "Pre-transaction validation",
"url": "https://api.example.com/blnk/hooks/pre",
"type": "PRE_TRANSACTION",
"active": true,
"timeout": 30,
"retry_count": 3
}
```
Create a transaction with. Blnk calls your hook URL when the transaction reaches the stage you registered, `PRE` or `POST`.
Confirm your endpoint receives an event with the expected payload and returns `2xx`.
```bash cURL wrap theme={"system"}
curl -X POST "http://YOUR_BLNK_INSTANCE_URL/transactions" \
-H "X-blnk-key: " \
-H "Content-Type: application/json" \
-d '{
"amount": 200,
"precision": 100,
"reference": "INV-2025-0008912",
"currency": "GBP",
"source": "@Funding",
"destination": "@UserWallet",
"description": "Wallet top-up"
}'
```
```typescript TypeScript wrap theme={"system"}
const response = await blnk.Transactions.create({
amount: 200,
precision: 100,
reference: 'INV-2025-0008912',
currency: 'GBP',
source: '@Funding',
destination: '@UserWallet',
description: 'Wallet top-up',
});
```
```go Go wrap theme={"system"}
transaction, resp, err := client.Transaction.Create(blnkgo.CreateTransactionRequest{
ParentTransaction: blnkgo.ParentTransaction{
Amount: 200,
Precision: 100,
Reference: "INV-2025-0008912",
Currency: "GBP",
Source: "@Funding",
Destination: "@UserWallet",
Description: "Wallet top-up",
},
})
```
Your hook endpoint should log or persist the delivery. If nothing arrives, confirm the hook is `active` and the URL is reachable from Blnk Core,
***
## Retries and timeouts
When your hook endpoint is unreachable, times out, or returns a non-`2xx` response, Blnk retries the delivery with backoff-up to the `retry_count` you set when registering the hook.
`timeout` sets how long Blnk waits for your endpoint on each attempt.
`retry_count` sets the maximum **additional** attempts after a failed delivery.
A delivery that failed while your receiver was down can arrive minutes later once the endpoint recovers.
Return a `2xx` response only after you have safely recorded or processed the event. Slow handlers can delay retries and increase duplicate deliveries under load.
***
## Related docs
Update, get, list, and delete hooks via the API reference.
Change URL, timeout, or active state.
Fetch a hook by id.
List PRE or POST hooks.
Remove a registered hook.
***
## Need help?
We are very happy to help you make the most of Blnk, regardless of whether it is your first time or you are switching from another tool.
To ask questions or discuss issues, please [contact us](mailto:support@blnkfinance.com) or [join our Discord community](https://discord.gg/7WNv94zPpx).
Sign up and manage your ledger with our back-office dashboard. You can invite teammates to collaborate and manage your ledger operations directly from the dashboard.