Transaction hooks

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.

Hook types

Blnk supports two hook types:

PRE_TRANSACTION: before a transaction is applied
POST_TRANSACTION: after a transaction is applied

Pre-transaction
Post-transaction

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"
  }
}

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.

POST_TRANSACTION payload

{
  "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

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
  }'

const response = await blnk.Hooks.create({
  name: 'Pre-transaction validation',
  url: 'https://api.example.com/blnk/hooks/pre',
  type: 'PRE_TRANSACTION',
  active: true,
  timeout: 30,
  retry_count: 3,
});

hook, resp, err := client.Hooks.Create(
    blnkgo.CreateHookRequest{
        Name: "Pre-transaction validation",
        URL: "https://api.example.com/blnk/hooks/pre",
        Type: blnkgo.HookTypePreTransaction,
        Active: true,
        Timeout: 30,
        RetryCount: 3,
    },
)

response = blnk.hooks.create({
  "name": "Pre-transaction validation",
  "url": "https://api.example.com/blnk/hooks/pre",
  "type": "PRE_TRANSACTION",
  "active": True,
  "timeout": 30,
  "retry_count": 3,
})

ApiResponse<JsonNode> response = blnk.hooks().create(
    CreateHookData.create()
        .name("Pre-transaction validation")
        .url("https://api.example.com/blnk/hooks/pre")
        .type(HookType.PRE_TRANSACTION)
        .active(true)
        .timeout(30)
        .retryCount(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.

201 Created

{
  "hook_id": "hk_890bdbc4-467f-4670-8424-5667e41daf29",
  "name": "Pre-transaction validation",
  "url": "https://api.example.com/blnk/hooks/pre",
  "type": "PRE_TRANSACTION",
  "active": true,
  "timeout": 30,
  "retry_count": 3
}

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"
  }'

const response = await blnk.Transactions.create({
  amount: 200,
  precision: 100,
  reference: 'INV-2025-0008912',
  currency: 'GBP',
  source: '@Funding',
  destination: '@UserWallet',
  description: 'Wallet top-up',
});

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",
        },
    },
)

response = blnk.transactions.create({
  "amount": 200,
  "precision": 100,
  "reference": "INV-2025-0008912",
  "currency": "GBP",
  "source": "@Funding",
  "destination": "@UserWallet",
  "description": "Wallet top-up",
})

ApiResponse<JsonNode> response = blnk.transactions().create(
    CreateTransactions.create()
        .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.

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.

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​Hook types

​Getting started

​Retries and timeouts

​Need help?

Hook types

Getting started

Retries and timeouts

Need help?