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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 for the full list of transaction event names.

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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.
PRE_TRANSACTION payload
{
  "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"
  }
}
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.

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Getting started

1

Register a hook

Register your webhook URL with the Hooks API:
Only the master key can create, update, view, list, or delete hooks. Regular API keys cannot, even if they include hooks scopes.
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
  }'
FieldDescription
nameHuman-readable label for operators and logs.
urlAbsolute HTTPS or HTTP URL that accepts requests from Blnk.
typeEither PRE_TRANSACTION or POST_TRANSACTION.
activeWhen false, Blnk skips this hook until you enable it again.
timeoutMaximum time in seconds Blnk waits for your endpoint to respond per attempt.
retry_countMaximum additional attempts after a failed delivery.
201 Created
{
  "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
}
2

Test the hook

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.
curl -X POST "http://YOUR_BLNK_INSTANCE_URL/transactions" \
  -H "X-blnk-key: <api-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"
  }'
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,

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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.
Update, get, list, and delete hooks via the API reference.

Update hooks

Change URL, timeout, or active state.

View hooks

Fetch a hook by id.

List hooks by type

List PRE or POST hooks.

Delete hooks

Remove a registered hook.

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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 or join our Discord community.