Interswitch Fintech Card Processing API

Process card debits, reversals, balance enquiries, and lien operations for fintech card programs.

Operations

Operation	Description
Debit	Charge a card account
Reversal	Reverse a previous debit
Enquiry	Check account balance
Lien	Place/release holds on funds

Endpoints

Endpoint	Method	Description
/api/v1/fintech/cards/debit	POST	Debit a card
/api/v1/fintech/cards/reversal	POST	Reverse a debit
/api/v1/fintech/cards/enquiry	POST	Balance enquiry
/api/v1/fintech/cards/lien	POST	Place a lien
/api/v1/fintech/cards/lien/release	POST	Release a lien

Card Debit

interface FintechDebitRequest {
  pan: string;                 // Card PAN (encrypted)
  amount: number;              // In kobo
  currency: string;            // '566' for NGN
  transactionRef: string;
  terminalId: string;
  merchantCode: string;
  description?: string;
}

interface FintechTransactionResponse {
  responseCode: string;
  responseDescription: string;
  transactionRef: string;
  amount: number;
  balance?: number;
  authCode?: string;
}

async function debitCard(
  data: FintechDebitRequest
): Promise<FintechTransactionResponse> {
  const headers = await getAuthHeaders();

  const response = await fetch(
    `${process.env.INTERSWITCH_BASE_URL}/api/v1/fintech/cards/debit`,
    {
      method: 'POST',
      headers: { ...headers, 'Content-Type': 'application/json' },
      body: JSON.stringify(data),
    }
  );

  return response.json();
}

Reversal

interface ReversalRequest {
  originalTransactionRef: string;  // Reference of the original debit
  amount: number;                  // Amount to reverse in kobo
  reversalRef: string;             // Unique reversal reference
  reason?: string;
}

async function reverseDebit(
  data: ReversalRequest
): Promise<FintechTransactionResponse> {
  const headers = await getAuthHeaders();

  const response = await fetch(
    `${process.env.INTERSWITCH_BASE_URL}/api/v1/fintech/cards/reversal`,
    {
      method: 'POST',
      headers: { ...headers, 'Content-Type': 'application/json' },
      body: JSON.stringify(data),
    }
  );

  return response.json();
}

Balance Enquiry

interface EnquiryRequest {
  pan: string;                 // Card PAN (encrypted)
  terminalId: string;
}

interface EnquiryResponse {
  responseCode: string;
  availableBalance: number;
  ledgerBalance: number;
  currency: string;
}

async function balanceEnquiry(
  data: EnquiryRequest
): Promise<EnquiryResponse> {
  const headers = await getAuthHeaders();

  const response = await fetch(
    `${process.env.INTERSWITCH_BASE_URL}/api/v1/fintech/cards/enquiry`,
    {
      method: 'POST',
      headers: { ...headers, 'Content-Type': 'application/json' },
      body: JSON.stringify(data),
    }
  );

  return response.json();
}

Lien Management

A lien places a hold on funds in a card account, preventing the cardholder from using those funds until the lien is released.

Place Lien

interface LienRequest {
  pan: string;                 // Card PAN
  amount: number;              // Lien amount in kobo
  lienRef: string;             // Unique lien reference
  expiryDate?: string;         // When lien auto-releases
  reason: string;
}

interface LienResponse {
  responseCode: string;
  responseDescription: string;
  lienRef: string;
  amount: number;
  expiryDate: string;
}

async function placeLien(
  data: LienRequest
): Promise<LienResponse> {
  const headers = await getAuthHeaders();

  const response = await fetch(
    `${process.env.INTERSWITCH_BASE_URL}/api/v1/fintech/cards/lien`,
    {
      method: 'POST',
      headers: { ...headers, 'Content-Type': 'application/json' },
      body: JSON.stringify(data),
    }
  );

  return response.json();
}

Release Lien

async function releaseLien(
  lienRef: string
): Promise<LienResponse> {
  const headers = await getAuthHeaders();

  const response = await fetch(
    `${process.env.INTERSWITCH_BASE_URL}/api/v1/fintech/cards/lien/release`,
    {
      method: 'POST',
      headers: { ...headers, 'Content-Type': 'application/json' },
      body: JSON.stringify({ lienRef }),
    }
  );

  return response.json();
}

Complete Processing Flow

// 1. Check balance before debit
const balance = await balanceEnquiry({
  pan: encryptedPan,
  terminalId: 'TERM001',
});

if (balance.availableBalance < 500000) {
  console.log('Insufficient funds');
  return;
}

// 2. Place lien (optional — for pending transactions)
const lien = await placeLien({
  pan: encryptedPan,
  amount: 500000,   // ₦5,000
  lienRef: `LIEN_${Date.now()}`,
  reason: 'Pending purchase authorization',
});

// 3. Debit the card
const debit = await debitCard({
  pan: encryptedPan,
  amount: 500000,
  currency: '566',
  transactionRef: `DEB_${Date.now()}_${crypto.randomUUID().slice(0, 8)}`,
  terminalId: 'TERM001',
  merchantCode: process.env.INTERSWITCH_MERCHANT_CODE!,
  description: 'Product purchase',
});

// 4. Release lien after successful debit
await releaseLien(lien.lienRef);

if (debit.responseCode === '00') {
  console.log('Debit successful:', debit.transactionRef);
} else {
  // 5. Reverse on failure
  const reversal = await reverseDebit({
    originalTransactionRef: debit.transactionRef,
    amount: 500000,
    reversalRef: `REV_${Date.now()}`,
    reason: 'Processing error',
  });
  console.log('Reversed:', reversal.responseCode);
}

Best Practices

1. Encrypt PAN data — Never send raw card numbers
2. Use liens for pending auth — Place liens for two-phase transactions
3. Always release liens — Even on failure, release holds
4. Unique references — Prevent duplicate debits with unique refs
5. Reversal timeframes — Process reversals promptly
6. Balance checks — Verify sufficient funds before debiting