Handling Deposits & Payouts in a Banking Application with Blnk • Blnk Developer Documentation

In this tutorial, you’ll learn how to implement deposits and payouts using the Blnk Ledger. You’ll explore and apply a variety of workflows to handle deposits and payouts seamlessly. This includes:

Understanding how to set up your ledger for effective tracking of deposits and payouts in your system.
Designing flexible workflows to accommodate various scenarios.
Ensuring reliable and accurate transaction processing for your users.

For this tutorial, we’ll use the Blnk TypeScript SDK for the implementation. If you prefer, you can also refer to the API reference for details on the available endpoints.

Prerequisites

Before starting, ensure you have:

A running Blnk Core instance (e.g. at http://localhost:5001).
An API key for Blnk (replace YOUR_API_KEY in the code examples). Required for authenticated requests.
Optionally, you can connect your Blnk Core to your Blnk Cloud workspace to view your ledger data.

To prepare for the rest of this tutorial, read our Building a Wallet with Blnk tutorial if you haven’t already. This resource will walk you through creating ledger balances for accounts in Blnk, which are essential for implementing deposits, withdrawals, and other financial operations covered later in this tutorial.

Handling deposits

When using Blnk to manage deposits, you can track the sources of your deposits—such as Stripe, Acme Bank, or others—directly in your ledger, enabling more detailed and accurate reporting. As illustrated in the map below, each source can be assigned to an internal balance, which will be reflected as the value of the source field in your transaction request. Fees (1% of the deposit amount, capped at $5) are deducted and tracked separately.

Explore the map yourself here From our map, we can verify:

The source of the deposit, for example, @AcmeBank if it originates from Acme Bank.
That the customer receives funds after the fees have been dededucted.
The deposit fees are tracked using the @Fees balance.

Deposits with fee processing

When recording a deposit with fee processing, we’ll use the Multiple Destinations feature to distribute the incoming funds between the customer’s balance and the fees balance. We’ll also apply inflight to validate the deposits against predefined business rules before finalizing the transaction.

TypeScript

async function recordDeposit(sourceId, customerBalanceId, amount, reference, stripePaymentId) {
  const blnk = await getBlnkInstance();
  
  // Calculate fee (1% capped at $5)
  const feePercentage = 0.01;
  const feeCap = 5;
  const calculatedFee = Math.min(amount * feePercentage, feeCap);
  const customerAmount = amount - calculatedFee;
  
  // Record the deposit with multiple destinations
  const transaction = await blnk.Transactions.create({
    amount: amount,                  // Total amount being deposited
    precision: 100,                 
    reference: reference,          
    currency: "USD",
    source: sourceId,               
    inflight: true,                  // Hold for verification
    destinations: [
      {
        identifier: customerBalanceId,
        distribution: `${customerAmount}`,                
        narration: "Deposit to your account"
      },
      {
        identifier: "@Fees",           
        distribution: `${calculatedFee}`, 
        narration: "Processing fee"
      }
    ],
    meta_data: {
      fee_amount: calculatedFee,
      stripe_payment_id: stripePaymentId
    },
    skip_queue: true                // Process immediately, bypassing queue
  });
  
  console.log(`Deposit recorded with ID: ${transaction.data.transaction_id}`);
  return transaction.data;
}

When you apply inflight to a multiple destinations transaction, all associated transactions—distributing funds to both destinations—are also placed in an inflight state until the commit or void is executed.

Verifying deposits based on business rules

Next, we’ll develop functions to process deposits according to the following business rules. In this tutorial, we’ll implement checks for two rules:

If the balance is blocked or frozen, the deposit should be voided.
If the deposit amount exceeds 1 million USD, it should remain in an inflight state, and a notification should be sent for further investigation.

Rule 1: Check if balance is blocked or frozen

TypeScript

async function processDepositBasedOnRules(transactionId) {
  const blnk = await getBlnkInstance();
  const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
  const apiKey = process.env.BLNK_API_KEY ?? '';

  const txnRes = await fetch(`${baseUrl}/transactions/${transactionId}`, {
    headers: { 'X-Blnk-Key': apiKey },
  });
  if (!txnRes.ok) throw new Error(await txnRes.text());
  const transaction = await txnRes.json();

  const destinations = transaction.destinations || [];
  const customerBalanceId = destinations[0]?.identifier;

  const balanceResponse = await blnk.LedgerBalances.get(customerBalanceId);
  const meta = balanceResponse.data?.meta_data || {};

  if (meta.status === 'frozen' || meta.status === 'blocked') {
    const metaUpdate = await fetch(`${baseUrl}/${transactionId}/metadata`, {
      method: 'POST',
      headers: {
        'X-Blnk-Key': apiKey,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        meta_data: { void_reason: `Account ${meta.status}` },
      }),
    });
    if (!metaUpdate.ok) throw new Error(await metaUpdate.text());

    const voidResult = await blnk.Transactions.updateStatus(transactionId, {
      status: 'void',
    });
    if (voidResult.status !== 200 || !voidResult.data) {
      throw new Error(voidResult.message ?? 'Failed to void transaction');
    }
    console.log(`Transaction ${transactionId} voided: account ${meta.status}`);
    return voidResult.data;
  }

  return await processDepositByAmount(transactionId);
}

Rule 2: Check amount rule

TypeScript

async function processDepositByAmount(transactionId) {
  const blnk = await getBlnkInstance();
  const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
  const apiKey = process.env.BLNK_API_KEY ?? '';

  const txnRes = await fetch(`${baseUrl}/transactions/${transactionId}`, {
    headers: { 'X-Blnk-Key': apiKey },
  });
  if (!txnRes.ok) throw new Error(await txnRes.text());
  const transaction = await txnRes.json();
  const amount = transaction.precise_amount;

  if (amount < 100000000) {
    const commit = await blnk.Transactions.updateStatus(transactionId, {
      status: 'commit',
    });
    if (commit.status !== 200 || !commit.data) {
      throw new Error(commit.message ?? 'Failed to commit transaction');
    }
    console.log(`Transaction ${transactionId} committed: amount below threshold`);
    return commit.data;
  }

  const metaRes = await fetch(`${baseUrl}/${transactionId}/metadata`, {
    method: 'POST',
    headers: {
      'X-Blnk-Key': apiKey,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      meta_data: {
        investigation_required: true,
        investigation_reason: 'Large deposit amount',
        flagged_at: new Date().toISOString(),
      },
    }),
  });
  if (!metaRes.ok) throw new Error(await metaRes.text());
  const flagged = await metaRes.json();

  await triggerLargeDepositHook(transactionId, amount);
  console.log(`Transaction ${transactionId} flagged for investigation: large amount`);
  return flagged;
}

Putting it all together

TypeScript

async function handleStripeDeposit(stripePaymentId, customerBalanceId, amount) {
  const blnk = await getBlnkInstance();
  
  // Step 1: Record the deposit with fee processing
  const reference = `stripe_${stripePaymentId}`;
  const depositData = await recordDeposit(
    "@Stripe", 
    customerBalanceId, 
    amount, 
    reference,
    stripePaymentId
  );
  
  // Step 2: Process the deposit based on business rules
  const result = await processDepositBasedOnRules(depositData.transaction_id);
  
  return {
    message: `Deposit processed with status: ${result.status}`
  };
}

Refunding deposits

To process refunds in your ledger and reverse a deposit:

TypeScript

async function refundDeposit(transactionId, reason = 'Customer requested refund') {
  const blnk = await getBlnkInstance();
  
  // Process the refund
  const refund = await blnk.Transactions.refund(transactionId);
  
  const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
  const apiKey = process.env.BLNK_API_KEY ?? '';
  const metaRes = await fetch(`${baseUrl}/${refund.data.refund_id}/metadata`, {
    method: 'POST',
    headers: {
      'X-Blnk-Key': apiKey,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      meta_data: { refund_reason: reason },
    }),
  });
  if (!metaRes.ok) throw new Error(await metaRes.text());

  console.log(`Deposit refunded: ${refund.data.refund_id}`);
  return refund.data;
}

Handling payouts

Payouts function similarly to deposits but in reverse. The Customer Balance serves as the source, while the Payout Destination and @Fees act as the destinations. Include @Fees if the customer incurs fees for payment processing.

From our map, we can verify:

The destination of the withdrawal.
That the customer receives funds after the fees have been deducted.
The deposit fees are tracked using the @Fees balance.

Path 1: Successful payouts

Here, the payout was successfully completed by your payout provider:

TypeScript

// Initiate a payout with inflight
async function initiatePayout(customerBalanceId, billsAmount, reference) {
  const blnk = await getBlnkInstance();

  // Calculate fee (0.5% with $1 minimum)
  const feePercentage = 0.005;
  const minFee = 1;
  const calculatedFee = Math.max(billsAmount * feePercentage, minFee);
  const totalAmount = billsAmount + calculatedFee;
  
  const payout = await blnk.Transactions.create({
    amount: totalAmount,
    precision: 100,
    reference: reference,
    description: "Payout for bills",
    currency: "USD",
    source: customerBalanceId,
    destinations: [
      {
        identifier: "@BillsPayment",
        distribution: `${billsAmount}`,
        narration: "Payout for bills"
      },
      {
        identifier: "@Fees",
        distribution: `${calculatedFee}`,
        narration: "Payout processing fee"
      }
    ],
    inflight: true,
    inflight_expiry_date: getExpiryDate(24), // Expires if no response is gotten in 24 hours
    meta_data: {
      payout_status: "pending",
      fee_amount: calculatedFee
    },
    skip_queue: true                         // Process immediately, bypassing queue
  });
  
  console.log(`Payout initiated: ${payout.data.transaction_id}`);
  return payout.data;
}

// Generate expiry date (hours from now)
function getExpiryDate(hours) {
  const date = new Date();
  date.setHours(date.getHours() + hours);
  return date.toISOString();
}

Commit based on feedback from payout provider

TypeScript

// Webhook handler for payment processor notifications
async function handlePaymentWebhook(webhookBody) {
  const { 
    event_type, 
    payout_id, 
    status, 
    transaction_reference 
  } = webhookBody;
  
  if (event_type === 'payment.success') {

    // Find the transaction by reference
    const searchResult = await blnk.Search.search({
      q: transaction_reference,
      query_by: "reference",
      filter_by: "status:=INFLIGHT"
    }, "transactions");

    // Get the parent transaction (transaction_id connecting both transactions together)
    const transaction = searchResult.data.hits[0].document;
    const transactionId = transaction.parent_transaction;

    const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
    const apiKey = process.env.BLNK_API_KEY ?? '';
    const metaRes = await fetch(`${baseUrl}/${transactionId}/metadata`, {
      method: 'POST',
      headers: {
        'X-Blnk-Key': apiKey,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        meta_data: {
          payout_status: 'confirmed',
          provider_payout_id: payout_id,
          confirmation_time: new Date().toISOString(),
        },
      }),
    });
    if (!metaRes.ok) throw new Error(await metaRes.text());

    const commit = await blnk.Transactions.updateStatus(transactionId, {
      status: 'commit',
    });
    if (commit.status !== 200 || !commit.data) {
      throw new Error(commit.message ?? 'Failed to commit payout');
    }
    console.log(`Payout confirmed and committed: ${transactionId}`);
    return {
      processed: true,
      transaction_id: transactionId,
    };
  }
}

How multiple destinations work

When using Multiple Destinations in a transaction (like in our tutorial), Blnk automatically generates a separate transaction record for each distribution. These individual records are linked together with the parent_transaction parameter. This structure organizes and connects all parts of a multi-destination transaction efficiently. A standout feature of this system is how actions on the parent_transaction affect the entire group:

Committing the parent_transaction automatically commits all associated distributions, confirming the full distribution.
Voiding the parent_transaction automatically voids all distributions, canceling the entire distribution in one step.

This unified approach simplifies managing complex transactions involving multiple recipients.

Path 2: Failed payouts

The payout is pending, but a failure message was received from the provider, resulting in the transaction being voided:

TypeScript

async function handlePaymentWebhook(webhookBody) {
  const { 
    event_type, 
    payout_id, 
    status, 
    transaction_reference 
  } = webhookBody;
  
  if (event_type === 'payment.failed') {

    // Find the transaction by reference
    const searchResult = await blnk.Search.search({
      q: transaction_reference,
      query_by: "reference",
      filter_by: "status:=INFLIGHT"
    }, "transactions");

    // Get the parent transaction (transaction_id connecting both transactions together)
    const transaction = searchResult.data.hits[0].document;
    const transactionId = transaction.parent_transaction;

    const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
    const apiKey = process.env.BLNK_API_KEY ?? '';
    const metaRes = await fetch(`${baseUrl}/${transactionId}/metadata`, {
      method: 'POST',
      headers: {
        'X-Blnk-Key': apiKey,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        meta_data: {
          payout_status: 'failed',
          provider_payout_id: payout_id,
          confirmation_time: new Date().toISOString(),
        },
      }),
    });
    if (!metaRes.ok) throw new Error(await metaRes.text());

    const voidResult = await blnk.Transactions.updateStatus(transactionId, {
      status: 'void',
    });
    if (voidResult.status !== 200 || !voidResult.data) {
      throw new Error(voidResult.message ?? 'Failed to void payout');
    }
    console.log(`Payout cancelled: ${transactionId}`);
    return {
      processed: true,
      transaction_id: transactionId,
    };
  }
}

Path 2: Successful payout but reversed

The payout was initially successful, with confirmation received from the provider, but the funds were reversed by the provider due to an inability to settle the transaction:

TypeScript

async function refundPayout(transactionId, reason = "Can't complete payout") {
  const blnk = await getBlnkInstance();
  
  // Process the refund
  const refund = await blnk.Transactions.refund(transactionId);
  
  const baseUrl = process.env.BLNK_BASE_URL ?? 'http://localhost:5001';
  const apiKey = process.env.BLNK_API_KEY ?? '';
  const metaRes = await fetch(`${baseUrl}/${refund.data.refund_id}/metadata`, {
    method: 'POST',
    headers: {
      'X-Blnk-Key': apiKey,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      meta_data: { refund_reason: reason },
    }),
  });
  if (!metaRes.ok) throw new Error(await metaRes.text());

  console.log(`Payout refunded: ${refund.data.refund_id}`);
  return refund.data;
}

Conclusion

You now have a basic deposits and payouts system powered by Blnk Ledger. It efficiently processes transactions while ensuring accurate records. The system is flexible and can be expanded with features like:

Automated handling of failed transactions
Custom withdrawal limits and approval workflows
Support for multiple funding sources
Real-time transaction monitoring and alerts

With Blnk’s transaction system, you can track and manage all money movements, building a solid foundation for your financial operations.

​Prerequisites

​Handling deposits

​Deposits with fee processing

​Verifying deposits based on business rules

​Rule 1: Check if balance is blocked or frozen

​Rule 2: Check amount rule

​Putting it all together

​Refunding deposits

​Handling payouts

​Path 1: Successful payouts

​Commit based on feedback from payout provider

​How multiple destinations work

​Path 2: Failed payouts

​Path 2: Successful payout but reversed

​Conclusion

Prerequisites

Handling deposits

Deposits with fee processing

Verifying deposits based on business rules

Rule 1: Check if balance is blocked or frozen

Rule 2: Check amount rule

Putting it all together

Refunding deposits

Handling payouts

Path 1: Successful payouts

Commit based on feedback from payout provider

How multiple destinations work

Path 2: Failed payouts

Path 2: Successful payout but reversed

Conclusion