Build your own mobile checkout implementation

With recent developments in legislation around the App Store, you can link users in the United States to an external checkout for purchases in iOS apps.

You can build your own Paddle Checkout implementation to quickly and securely collect for payment for digital products outside your app. Customers tap a button in your app to open your checkout implementation, then they're redirected to your app when they complete their purchase.

What are we building?

In this tutorial, we'll use Paddle.js and the Paddle SDKs to create a custom checkout implementation as part of an external purchase flow for in-app purchases in iOS apps.

We'll walk through handling fulfillment using the RevenueCat x Paddle integration or webhooks.

What's not covered

This tutorial doesn't cover:

• Handling authentication
  We assume you already have a way to identify your users, like Firebase or Sign in with Apple.
• Native in-app purchases
  We'll launch Paddle Checkout in Safari then redirect users back to your app. Like the App Store, Paddle Checkout supports Apple Pay with no additional setup, plus other popular payment options.
• Subscription lifecycle management
  You can use Paddle to handle all parts of the subscription lifecycle, including updating payment methods and canceling subscriptions using the prebuilt customer portal. We cover that elsewhere in our docs.

Before you begin

Sign up for Paddle

You'll need a Paddle account to get started. You can sign up for two kinds of account:

• Sandbox — for testing and evaluation
• Live — for selling to customers

For this tutorial, we recommend signing up for a sandbox account. You can transition to a live account later when you've built your integration and you're ready to start selling.

If you sign up for a live account, you'll need to complete account verification. This is where we ask for some information from you to make sure that we can work together.

Prep your iOS development environment

As part of our tutorial, we're going to update our app to include a link to the page on your website where you set up Paddle.js. You'll need:

• Some knowledge of iOS development, access to your iOS project, and Xcode on macOS.
• A correctly configured URL scheme so you can redirect users back to your app.

You don't need to make changes to your iOS app to set up Paddle.js on your website, so you can come back to this later if you're working with a separate iOS developer.

Overview

Build your own Paddle Checkout implementation to link out for in-app purchases in six steps:

1. Map your product catalog
   Create products and prices in Paddle that match your in-app purchase options.
2. Add Paddle.js to your website
   Include Paddle.js on a page on your website, then handle the post-purchase redirect back to your app.
3. Create a transaction in Paddle
   Build logic in your backend to create a customer and a transaction in Paddle, ready for checkout.
4. Add a checkout button to your app
   Create a button that creates a transaction in Paddle and opens your checkout.
5. Handle fulfillment and provisioning using webhooks
   Use RevenueCat or process webhooks to fulfill purchases after a customer completes a checkout.
6. Take a test payment
   Make a test purchase to make sure your purchase flow works correctly.

Map your product catalog

Before we implement Paddle Checkout, we need to set up our product catalog in Paddle to match the in-app purchases offered in-app.

Model your pricing

A complete product in Paddle is made up of two parts:

• A product entity that describes the item, like its name, description, and an image.
• At least one related price entity that describes how much and how often a product is billed.

You can create as many prices for a product as you want to describe all the ways they're billed.

In this example, we'll create a single product and single price for a one-time item called Lifetime Access.

Create products and prices

You can create products and prices using the Paddle dashboard or the API.

Add Paddle.js to your website

Paddle.js is a lightweight JavaScript library that lets you build rich, integrated billing experiences using Paddle. We can use Paddle.js to securely open a checkout, capture payment information, and launch our success workflow.

When you add Paddle.js to a page, you can redirect to that page and append a _ptxn query parameter with the value of a transaction ID in Paddle to launch a checkout automatically.

You can create a new page, or add to an existing one like your homepage.

Include and initialize Paddle.js

pnpm add @paddle/paddle-js

yarn add @paddle/paddle-js

npm install @paddle/paddle-js

import { initializePaddle } from '@paddle/paddle-js';

const paddle = await initializePaddle({
  token: 'CLIENT_SIDE_TOKEN'
});

<script src="https://cdn.paddle.com/paddle/v2/paddle.js"></script>
<script type="text/javascript">
  Paddle.Initialize({
    token: "CLIENT_SIDE_TOKEN"
  });
</script>

Get a client-side token

Client-side tokens are for authenticating with Paddle in your frontend. We need one to securely open Paddle Checkout.

Build a success workflow

After users complete a purchase successfully, we need to redirect users back to our app.

To do this, we can use an event callback function. Paddle.js emits events throughout the checkout process when key things happen. An event callback function is some code that we run when a specific event occurs.

In our case, when Paddle.js emits a checkout.completed event, we're going to redirect to a screen in our app.

import { initializePaddle } from '@paddle/paddle-js';
import { CheckoutEventNames, PaddleEventData } from '@paddle/paddle-js';

const paddle = await initializePaddle({
  token: 'CLIENT_SIDE_TOKEN',
  eventCallback: (event: PaddleEventData) => {
    if (event.name === CheckoutEventNames.CHECKOUT_COMPLETED) {

      setTimeout(() => {
        window.location.href = `myapp://example-redirect?transactionId=${event.data?.id}`;
      }, 3000);
    }
  }
});

<script src="https://cdn.paddle.com/paddle/v2/paddle.js"></script>
<script type="text/javascript">
  Paddle.Initialize({
    token: "CLIENT_SIDE_TOKEN",
    eventCallback: function(event) {
      if (event.name === 'checkout.completed') {
        setTimeout(function() {
          let transactionId = event.data && event.data.id ? event.data.id : '';
          window.location.href = 'myapp://example-redirect?transactionId=' + transactionId;
        }, 3000);
      }
    }
  });
</script>

When you're done, deploy your page to your website.

Set your default payment link

Your default payment link is a quick way to open Paddle Checkout for a transaction. It's also used in emails from Paddle that let customers manage purchases that are recurring. You need to set a default payment link before you can launch a checkout.

We'll set our default payment link to the page where we just added Paddle.js:

Create a transaction in Paddle

Transactions are the central billing entity in Paddle. They capture and calculate revenue for a customer purchase, and represent what they see when they open a checkout.

We'll create a transaction with details about what our customer is purchasing in our backend, then extract the checkout link to launch a checkout. We can use the transaction ID as a central identifier for this purchase throughout the journey.

Install Paddle

First, add the Paddle SDK to your backend. Paddle has SDKs for Node.js, Python, PHP, and Go.

pnpm add @paddle/paddle-node-sdk

yarn add @paddle/paddle-node-sdk

npm install @paddle/paddle-node-sdk

Get an API key

API keys are for authenticating with Paddle in your backend. We need one to create a transaction.

Set up the endpoint

You need to set up an endpoint to call from your iOS app to create the transaction in Paddle and return the checkout link.

const express = require('express');
const cors = require('cors');
const bodyParser = require('body-parser');

// Import Paddle SDK
const { Paddle } = require('@paddle/paddle-node-sdk');

// Express setup
const app = express();
const PORT = process.env.PORT || 3000;
app.use(cors());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
require('dotenv').config();

// Initialize Paddle
// Assumes you have a Paddle API key in the .env file
const paddle = new Paddle(process.env.PADDLE_API_KEY);

app.post("/paddle/create-transaction", async (req, res) => {
  try {
  // You will insert code here in the next steps

  } catch (error) {
    console.error('Error creating transaction:', error);
    return res.status(500).json({ error: error.message });
  }
});

// Start server
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Create a customer

If the user is signed in to your app, create a customer in Paddle for them.

Customers are lightweight entities that hold high-level details, like name and email address. They have related address and business entities.

const express = require('express');
const cors = require('cors');
const bodyParser = require('body-parser');

// Import Paddle SDK
const { Paddle } = require('@paddle/paddle-node-sdk');

// Express setup
const app = express();
const PORT = process.env.PORT || 3000;
app.use(cors());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
require('dotenv').config();

// Initialize Paddle
const paddle = new Paddle(process.env.PADDLE_API_KEY);

app.post("/paddle/create-transaction", async (req, res) => {
  try {
  // 1. Fetch or create a Paddle customer
    const { userId } = req.body;

    const existingUser = await User.findOne({ where: { id: userId } });

    if (!existingUser) {
      return res.status(404).json({ error: 'User not found' });
    }

    // Check if customer already exists in Paddle
    if (!existingUser.paddleCustomerId) {
      const customer = await paddle.customers.create({
        email: existingUser.email,
        name: existingUser.name
      });

      // Update the user with the Paddle customer ID
      await existingUser.update({ paddleCustomerId: customer.id });
      existingUser.paddleCustomerId = customer.id;
    }
  } catch (error) {
    console.error('Error creating transaction:', error);
    return res.status(500).json({ error: error.message });
  }
});

// Start server
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Create a transaction and extract the URL

To set up a checkout, create a transaction with:

• The customer ID of this customer.
• The items the customer is purchasing, which include the price ID we set up earlier and a quantity for each.

Once created, extract the checkout.url and return it to your app.

const cors = require('cors');
const bodyParser = require('body-parser');

// Import Paddle SDK
const { Paddle } = require('@paddle/paddle-node-sdk');

// Express setup
const app = express();
const PORT = process.env.PORT || 3000;
app.use(cors());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
require('dotenv').config();

// Initialize Paddle
const paddle = new Paddle(process.env.PADDLE_API_KEY);

app.post("/paddle/create-transaction", async (req, res) => {
  try {
  // 1. Fetch or create a Paddle customer
    const { userId } = req.body;

    const existingUser = await User.findOne({ where: { id: userId } });

    if (!existingUser) {
      return res.status(404).json({ error: 'User not found' });
    }

    // Check if customer already exists in Paddle
    if (!existingUser.paddleCustomerId) {
      const customer = await paddle.customers.create({
        email: existingUser.email,
        name: existingUser.name
      });

      // Update the user with the Paddle customer ID
      await existingUser.update({ paddleCustomerId: customer.id });
      existingUser.paddleCustomerId = customer.id;
    }

    // 2. Create the transaction
    // (Optional) Grab RevenueCat metadata field ID passed from the iOS app.
    // You can use any name to pass through. We use revenuecatId.
    const { revenuecatId } = req.body;

    // Grab the items from the request body
    // This is an array of objects with a price_id and quantity for each item the customer is purchasing
    const { items } = req.body;

    if (!Array.isArray(items) || items.length === 0) {
      return res.status(400).json({ error: "Items array is required and can't be empty" });
    }

    // Create the transaction
    const transaction = await paddle.transactions.create({
      customer_id: existingUser.paddleCustomerId,
      items: items,
      collection_mode: 'automatic', // Default that means checkout is created

      custom_data: {
        rc_user_id: revenuecatId // (Optional) If using Revenuecat, pass the metadata field ID.
      }
    });

    // Return the checkout link to the iOS app
    res.json({
      checkoutUrl: transaction.checkout.url
    });
  } catch (error) {
    console.error('Error creating transaction:', error);
    return res.status(500).json({ error: error.message });
  }
});

// Start server
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Add a checkout button to your app

Now, update your iOS app to add a button that:

1. Checks to see if in-app purchases are allowed on the device
2. Checks to see if a user already purchased the item.
3. Calls your backend endpoint to create a Paddle transaction.
4. Opens the checkout link returned by your endpoint in Safari.

Handle fulfillment and provisioning

When a customer completes a purchase, they'll be redirected back to your app. At this point, you need to handle fulfillment and unlock the features they bought.

app.post("/paddle/webhooks", express.raw({ type: 'application/json' }), async (req, res) => {
  try {
    // You can verify the webhook signature here
    // We don't cover this in the tutorial but it's best practice to do so
    // https://developer.paddle.com/webhooks/signature-verification

    const payload = JSON.parse(req.body.toString());
    const { data, event_type } = payload;
    const occurredAt = payload.occurred_at;

    // Listen for vital events from Paddle
    switch (event_type) {
      // 1. Record transactions in the database

      // Handle a new transaction
      // You can create a Transaction database to store records and associate them to a user
      case 'transaction.created':
        // Find the user associated with this transaction
        const userForTransaction = await User.findOne({ where: { paddleCustomerId: data.customer_id } });

        if (userForTransaction) {
          await Transaction.create({
            transactionId: data.id,
            userId: userForTransaction.id,
            subscriptionId: data.subscription_id,
            status: data.status,
            amount: data.amount,
            currencyCode: data.currency_code,
            occurredAt: occurredAt
          });
        }
        break;

      // Handle a completed transaction
      // If you have a Transaction database, you can update the transaction record
      case 'transaction.completed':

        // Find the transaction by its ID
        const completedTransaction = await Transaction.findOne({
          where: { transactionId: data.id }
        });

        if (completedTransaction) {
          await completedTransaction.update({
            status: data.status,
            subscriptionId: data.subscription_id,
            invoiceId: data.invoice_id,
            invoiceNumber: data.invoice_number,
            billedAt: data.billed_at,
            updatedAt: data.updated_at
          });
        }
        break;
    }

    res.json({ received: true });
  } catch (error) {
    console.error('Error processing webhook:', error);
    return res.status(500).json({ error: error.message });
  }
});

app.post("/paddle/webhooks", express.raw({ type: 'application/json' }), async (req, res) => {
  try {
    // You can verify the webhook signature here
    // We don't cover this in the tutorial but it's best practice to do so
    // https://developer.paddle.com/webhooks/signature-verification

    const payload = JSON.parse(req.body.toString());
    const { data, event_type } = payload;
    const occurredAt = payload.occurred_at;

    // Listen for vital events from Paddle
    switch (event_type) {
      // 1. Record transactions in the database

      // Handle a new transaction
      // You can create a Transaction database to store records and associate them to a user
      case 'transaction.created':
        // Find the user associated with this transaction
        const userForTransaction = await User.findOne({ where: { paddleCustomerId: data.customer_id } });

        if (userForTransaction) {
          await Transaction.create({
            transactionId: data.id,
            userId: userForTransaction.id,
            subscriptionId: data.subscription_id,
            status: data.status,
            amount: data.amount,
            currencyCode: data.currency_code,
            occurredAt: occurredAt
          });
        }
        break;

      // Handle a completed transaction
      // If you have a Transaction database, you can update the transaction record
      case 'transaction.completed':

        // Find the transaction by its ID
        const completedTransaction = await Transaction.findOne({
          where: { transactionId: data.id }
        });

        if (completedTransaction) {
          await completedTransaction.update({
            status: data.status,
            subscriptionId: data.subscription_id,
            invoiceId: data.invoice_id,
            invoiceNumber: data.invoice_number,
            billedAt: data.billed_at,
            updatedAt: data.updated_at
          });

          // 2. Provision access to your app
          // Fetch the user associated with this transaction
          const user = await User.findOne({ where: { id: completedTransaction.userId } });

          if (user) {
            // Fetch the items from the transaction
            const purchasedItems = data.items || [];

            // Add what access the user has based on the items they purchased
            // For this example, we're using access permissions and storing them in the user model on an accessPermissions field
            // We also map the Paddle product IDs to the access permissions
            // In a real app, you could use a database table for this mapping

            // Get existing permissions to see if any first
            const accessPermissions = user.accessPermissions ? JSON.parse(user.accessPermissions) : {};

            // Map product IDs to access permissions
            // We add an additional product as an example of how you can handle multiple
            const productToPermission = {
              'pro_01h1vjes1y163xfj1rh1tkfb65': 'lifetimeAccess',
              'pro_01gsz97mq9pa4fkyy0wqenepkz': 'temporaryAccess'
            }

            purchasedItems.forEach(({ price }) => {
              const permissionKey = productToPermission[price.product_id];
              if (permissionKey) accessPermissions[permissionKey] = true;
            });

            // Update the user with their new access permissions
            await user.update({
              accessPermissions: JSON.stringify(accessPermissions),
            });
          }
        }
        break;
    }

    res.json({ received: true });
  } catch (error) {
    console.error('Error processing webhook:', error);
    return res.status(500).json({ error: error.message });
  }
});

Test the complete flow

We're now ready to test the complete purchase flow end-to-end. If you're using a sandbox account, you can take a test payment using our test card details:

Email address

An email address you own

Country

Any valid country supported by Paddle

ZIP code (if required)

Any valid ZIP or postal code

Card number

4242 4242 4242 4242

Name on card

Any name

Expiration date

Any valid date in the future.

Security code

100

Next steps

That's it. Now you've built a purchase workflow that links out to Paddle Checkout, you might like to hook into other features of the Paddle platform.

Learn more about Paddle

When you use Paddle, we take care of payments, tax, subscriptions, and metrics with one unified platform. Customers can self-serve with the portal, and Paddle handles any order inquiries for you.

Build a web checkout

Our tutorial creates a transaction, then passes that transaction to Paddle.js. You can also use Paddle.js to build pricing pages and signup flows on the web, then redirect people to your app.

Build advanced subscription functionality

Paddle Billing is designed for subscriptions as well as one-time items. You can use Paddle to build workflows to pause and resume subscriptions, flexibly change billing dates, and offer trials.