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Overview

Transactions enable money movement between two or more balances. These can be payments, transfers, settlements, internal treasury management, etc. All transactions in Blnk are recorded with the double entry principle — every transaction has a source and a corresponding destination. Transactions happen between balances, and balances are created within ledgers. In this guide, you’ll learn about:
  1. Transaction properties
  2. Recording a transaction
  3. Verifying transactions

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Transaction properties

  1. Immutability: Once recorded, transactions in Blnk cannot be modified or deleted. This fundamental property ensures the integrity and reliability of your transaction history, preventing any unauthorized alterations. See also: Transaction hashing
  2. Idempotency: Each transaction in Blnk produces the same result whether executed once or multiple times. This is crucial for maintaining data consistency, especially during network failures or system retries.
    Blnk implements idempotency by requiring a unique reference for every transaction. This reference serves as a transaction identifier, preventing duplicate processing and ensuring consistent outcomes.

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Recording a transaction

To record a transaction, call the record-transaction endpoint: 
POST http://YOUR_BLNK_INSTANCE_URL/transactions
With the following request body: 
curl -X POST "http://YOUR_BLNK_INSTANCE_URL/transactions" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": 750,
    "reference": "ref_001adcfgf",
    "currency": "USD",
    "precision": 100,
    "source": "@FundingPool",
    "destination": "bln_ebcd230f-6265-4d4a-a4ca-45974c47f746",
    "description": "Fund with starting balance amount",
    "allow_overdraft": true,
    "skip_queue": false,
    "meta_data": {}
  }'
If this is your first transaction, the participating balances will start at 0. To ensure the transaction is successful, enable overdrafts as shown above, allowing the source balance to go negative.Learn more about Overdrafts and Negative Balances.
  • Request
  • Response
FieldDescriptionRequiredType
amountThe transaction amount.Yesfloat
referenceYour unique reference to ensure idempotency.Yesstring
currencyShort code for your asset class.Yesstring
precisionPrecision for the currency/asset passed. See also: PrecisionNoint64
sourceSender’s balance IDYesstring
destinationRecipient’s balance ID.Yesstring
descriptionDescription or narration of the transaction.Nostring
meta_dataCustom data associated with the transactionNoobject
Passing detailed data with the meta_data object is encouraged; it provides you with 360-degree insights about each transaction record. Examples of data you can pass include sender_name, account_number, bank_name, receiver_name, payment_id, ip_address, location, payment_method, etc.
Next, you can view a list of all transactions in your ledger:
bash
blnk transactions list

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Verifying transactions

After recording a transaction, you can verify its status using different methods depending on whether you’re using the default queue system or the skip queue feature.

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Verifying transactions with queue (default)

When using the default queue system, every transaction starts as QUEUED. To verify your transaction status, you have two options:
  1. Webhooks: Blnk sends webhook notifications when transaction states change.
  2. Direct API calls: Query the transaction status using the reference or transaction ID. See below:
    • By reference (direct endpoint)
    • By transaction ID
    Blnk appends a _q suffix to your original reference after processing a QUEUED transaction. To verify the updated status, retrieve the transaction using your original reference plus the _q suffix.
    curl -X GET "http://YOUR_BLNK_INSTANCE_URL/transactions/reference/{reference}" \
  -H "X-blnk-key: <api-key>"

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Verifying transactions without queue (skip queue)

When using skip_queue: true, transactions are processed immediately and you can verify them from the direct response. Learn more about skip queue. 
curl -X POST "http://YOUR_BLNK_INSTANCE_URL/transactions" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": 750,
    "reference": "ref_001adcfgf",
    "currency": "USD",
    "precision": 100,
    "source": "@FundingPool",
    "destination": "bln_ebcd230f-6265-4d4a-a4ca-45974c47f746",
    "description": "Fund with starting balance amount",
    "allow_overdraft": true,
    "skip_queue": true
  }'
The response immediately shows the final status (INFLIGHT, APPLIED, or REJECTED), allowing you to confirm the transaction result without waiting for webhooks or additional API calls.
When using skip_queue: true, you may encounter lock errors if multiple transactions are processed simultaneously on the same balance. Learn how to handle these scenarios in our Handling Hot Balances guide.

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Discarded transactions

A discarded transaction is not recorded in the ledger. Blnk discards transactions for one reason:
  1. Duplicate reference: Your new transaction reference matches an existing reference in your ledger. Blnk requires unique reference values per transaction. Options are timestamps (e.g. UNIX timestamp), random string or UUID (e.g. ref_e55c4f33-bff7-4c30-9b9f-5d2d10a29b7a), or a business identifier like an order_id.
Make sure your request body match the Blnk Ledger API specifications. For example, avoid passing apply_overdraft instead of allow_overdraft.

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Managing insufficient funds

Available in version 0.11.0 and later. For versions 0.10.8 and older, see our insufficient funds guide.
Blnk performs comprehensive balance checks before processing any transaction to ensure you have sufficient funds available. The system computes an available balance by calculating balance - inflight_debit_balance on the source balance.
Inflight debit balance is the amount waiting to be deducted from the source balance from inflight transactions. Learn more: Inflight transactions.
If the transaction amount is more than the available balance, the source has insufficient funds and:
  1. The transaction is rejected and status is recorded as REJECTED.
  2. A webhook notification to inform your system of the rejected transaction and a reason in its meta_data.

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Using overdrafts

If you want a transaction to proceed even when it exceeds the available balance, you can enable overdrafts by setting allow_overdraft: true in your transaction request.

Learn about overdrafts

Detailed guide on managing overdrafts and negative balances

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Dive deeper

Transaction lifecycle

Learn how transactions move through different states from creation to completion

Understanding precision

Master decimal handling and precision for accurate financial calculations

Transaction statuses

Understand what each transaction status means and when they occur

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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.
Tip: Connect to Blnk Cloud to see your Core data.You can view your transactions, manage identities, create custom reports, invite other team members to collaborate, and perform operations on your Core — all in one dashboard.Check out Blnk Cloud →