Building a Multi-Vendor Store with Paystack

// Cart: items from multiple vendors
// [{ vendor_id, items, subtotal }]

app.post('/api/checkout', async (req, res) => {
  var { cart, email } = req.body;
  var commissionRate = 0.10;
  var total = cart.reduce((s, v) => s + v.subtotal, 0);

  // Build subaccounts list for the split
  var splitSubaccounts = await Promise.all(
    cart.map(async (vendorCart) => {
      var vendor = await db.vendors.findById(vendorCart.vendor_id);
      var vendorShare = Math.round(vendorCart.subtotal * (1 - commissionRate) * 100); // kobo
      return { subaccount: vendor.subaccount_code, share: vendorShare };
    })
  );

  // Create Transaction Split
  var splitRes = await fetch('https://api.paystack.co/split', {
    method: 'POST',
    headers: { Authorization: 'Bearer ' + process.env.PAYSTACK_SECRET_KEY, 'Content-Type': 'application/json' },
    body: JSON.stringify({
      name: 'Cart ' + Date.now(),
      type: 'flat',
      currency: 'NGN',
      subaccounts: splitSubaccounts,
      bearer_type: 'account',
    }),
  });
  var splitData = await splitRes.json();

  // Initialize transaction with split
  var txRes = await fetch('https://api.paystack.co/transaction/initialize', {
    method: 'POST',
    headers: { Authorization: 'Bearer ' + process.env.PAYSTACK_SECRET_KEY, 'Content-Type': 'application/json' },
    body: JSON.stringify({
      email,
      amount: total * 100,
      split_code: splitData.data.split_code,
      metadata: { cart: cart.map(v => ({ vendor_id: v.vendor_id, subtotal: v.subtotal })) },
    }),
  });
  var txData = await txRes.json();
  res.json({ authorization_url: txData.data.authorization_url });
});

This guide is part of the Paystack split payments guide.

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