Take a Card Payment with the Web Payments SDK

Use the Web Payments SDK Quickstart sample project to set up a web application that is integrated with the Square Web Payments SDK for taking payments.

The following video demonstrates how to build an end-to-end payment flow with the credit card payment method, and shows the code you use to build the flow. For an optimal viewing experience, expand the video window to a desired size or watch the video on YouTube. For a detailed overview of building with the card payment method, see the following sections in this topic.

To accept a card payment from a buyer, you need a web client where the buyer enters payment card information and a backend that takes a payment with the card. The SDK produces a secure one-time-use payment token based on the card. Your web client sends the payment token to your backend where the payment is taken. In summary, a payment is taken with these steps:

1. Generate a payment token - Use the Web Payments SDK client library to render a card entry form and generate a payment token that your web client sends to your backend server.
2. Create a payment with the token - On your backend, use the Square Payments API to create a payment.

This topic shows you where to add HTML and JavaScript to your web client to integrate the Web Payments SDK and take a payment on your backend.

You can find a full example of the Card payment code in GitHub.

The following shows the card payment method rendered in a web page:

The payment method doesn't initially render input fields for the name or the billing address. When you initially set up the payment method, you don't need to include input fields for contact information (name and billing information). You only need to first set up payment processing with fields for the credit card number, expiration date, the CVV (card verification value), and if required for your region, a zip or postal code.

The form automatically recognizes the credit card type as soon as you enter the credit card number, and the form updates the credit card icon as a result to reflect the type being used.

To request the buyer to provide contact information and other additional information for the payment, you can add additional payment form fields to the page layout.

Start by cloning the quickstart project template into a folder on your computer.

Test the application

The project template isn't initially integrated with the SDK and doesn't render the card payment form.

1. Follow the GitHub repo README instructions to get the development server running.

2. Open a browser to http://localhost:3000 to verify that the server is running.

   Your web page looks like the following page:

   

The walkthrough asks you to update the code in these project files:

• The public/index.html file is an empty static HTML page where you add the Web Payments SDK and application logic.
• The public/app.css file is the stylesheet that contains some preset styles to help with the page layout.
• The top-level server.js file contains the server call to the CreatePayment endpoint for charging the payment source. The quickstart application must include server.js to make the server call; otherwise, the application cannot create a payment. The quickstart project also includes tests in the server.tests.js file.

// If you're a non-US account, you must change the currency to match the country in which
// you're accepting the payment.
currency: 'USD',

Get the web client ready to accept a payment card and send the resulting token to the server component of the quickstart application.

You need your Sandbox credentials because the quickstart application is configured to send requests to the Square Sandbox instead of your production Square account.

1. Open the Developer Dashboard and click the plus symbol under Applications to create a new application.
2. Open the application and choose the Credentials page.
3. Set the Developer Dashboard mode to Sandbox to get a Sandbox application ID.
4. Copy the Sandbox Application ID and Sandbox Access Token.
5. Choose the Locations page and copy the Sandbox location ID.
6. Paste the application ID, location ID, and Sandbox access token into a temporary text file.

The quickstart server code calls the CreatePayment endpoint and needs to be updated to use your Sandbox access token.

1. In the project root folder, create a copy of the .env.example file and name it .env.sandbox.

2. Open the copied file to edit.

3. Define SQUARE_ACCESS_TOKEN with your Sandbox access token from the Developer Dashboard.

   SQUARE_ACCESS_TOKEN={SANDBOX_ACCESS_TOKEN}

4. Restart your server for the Sandbox test environment (npm run dev) to use this new value.

You need a Sandbox application ID and Sandbox location ID in the following steps. You should paste these values into a text file or leave the Developer Dashboard open in another browser tab so that you can copy the values as needed.

1. Replace the body of public/index.html with this HTML:

    <form id="payment-form">
      
      <button id="card-button" type="button">Pay $1.00</button>
    </form>

   This HTML adds an element (``) that the Web Payments SDK attaches the card element to and adds a button that starts the tokenization process.

The following JavaScript instantiates the SDK, provides the Card payment object, attaches it to the page, and generates the payment token:

1. Add an empty <script> tag to the <head> of index.html after <script type="text/javascript" src="https://sandbox.web.squarecdn.com/v1/square.js"></script>.

   <script>
   </script>

2. Add the following global constants inside the <script> tag, substituting the IDs from the Developer Dashboard for the placeholder ({YOUR_SANDBOX_APPLICATION_ID} and {YOUR_SANDBOX_LOCATION_ID}) values:

   const appId = '{YOUR_SANDBOX_APPLICATION_ID}';
   const locationId = '{YOUR_SANDBOX_LOCATION_ID}';

3. Add the following code inside the <script> tag:

    async function initializeCard(payments) {
      const card = await payments.card();
      await card.attach('#card-container'); 
      return card; 
    }
   
   document.addEventListener('DOMContentLoaded', async function () {
     if (!window.Square) {
       throw new Error('Square.js failed to load properly');
     }
     const payments = window.Square.payments(appId, locationId);
     let card;
     try {
       card = await initializeCard(payments);
     } catch (e) {
       console.error('Initializing Card failed', e);
       return;
     }
   
     // Step 5.2: create card payment
   });

The code does the following:

1. Initializes the Web Payments SDK by calling Square.payments(appId, locationId).
2. Initializes the Card payment method by calling the Payments .card() method and attaching the payment method to the page DOM by calling the Card .attach() method.

Test the application

1. Navigate to http://localhost:3000/ in your browser.

   

Before you can take a payment, you need to configure your developer credentials, which can be found in the Developer Dashboard.

1. Add the following code after the initializeCard function inside the <script> tag:

    // Call this function to send a payment token, buyer name, and other details
    // to the project server code so that a payment can be created with 
    // Payments API
    async function createPayment(token) {
      const body = JSON.stringify({
        locationId,
        sourceId: token,
        idempotencyKey
      });
      const paymentResponse = await fetch('/payment', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
        },
        body,
      });
      if (paymentResponse.ok) {
        return paymentResponse.json();
      }
      const errorBody = await paymentResponse.text();
      throw new Error(errorBody);
    }
   
    // This function tokenizes a payment method. 
    // The ‘error’ thrown from this async function denotes a failed tokenization,
    // which is due to buyer error (such as an expired card). It's up to the
    // developer to handle the error and provide the buyer the chance to fix
    // their mistakes.
    async function tokenize(paymentMethod) {
      const tokenResult = await paymentMethod.tokenize();
      if (tokenResult.status === 'OK') {
        return tokenResult.token;
      } else {
        let errorMessage = `Tokenization failed-status: ${tokenResult.status}`;
        if (tokenResult.errors) {
          errorMessage += ` and errors: ${JSON.stringify(
            tokenResult.errors
          )}`;
        }
        throw new Error(errorMessage);
      }
    }
   
    // Helper method for displaying the Payment Status on the screen.
    // status is either SUCCESS or FAILURE;
    function displayPaymentResults(status) {
      const statusContainer = document.getElementById(
        'payment-status-container'
      );
      if (status === 'SUCCESS') {
        statusContainer.classList.remove('is-failure');
        statusContainer.classList.add('is-success');
      } else {
        statusContainer.classList.remove('is-success');
        statusContainer.classList.add('is-failure');
      }
   
      statusContainer.style.visibility = 'visible';
    }

2. Add the following code to the DOMContentLoaded event listener in step 4.3 by replacing // Step 5.2: create card payment with the following code:

    async function handlePaymentMethodSubmission(event, paymentMethod) {
      event.preventDefault();
   
      try {
        // disable the submit button as we await tokenization and make a
        // payment request.
        cardButton.disabled = true;
        const token = await tokenize(paymentMethod);
        const paymentResults = await createPayment(token);
        displayPaymentResults('SUCCESS');
   
        console.debug('Payment Success', paymentResults);
      } catch (e) {
        cardButton.disabled = false;
        displayPaymentResults('FAILURE');
        console.error(e.message);
      }
    }
   
    const cardButton = document.getElementById(
      'card-button'
    );
    cardButton.addEventListener('click', async function (event) {
      await handlePaymentMethodSubmission(event, card);
    });

The complete DOMContentLoaded Event Listener should look like the following code:

document.addEventListener('DOMContentLoaded', async function () {
  if (!window.Square) {
    throw new Error('Square.js failed to load properly');
  }

  const payments = window.Square.payments(appId, locationId);
  let card;
  try {
    card = await initializeCard(payments);
  } catch (e) {
    console.error('Initializing Card failed', e);
    return;
  }

  async function handlePaymentMethodSubmission(event, paymentMethod) {
    event.preventDefault();

    try {
      // disable the submit button as we await tokenization and make a
      // payment request.
      cardButton.disabled = true;
      const token = await tokenize(paymentMethod);
      const paymentResults = await createPayment(token);
      displayPaymentResults('SUCCESS');

      console.debug('Payment Success', paymentResults);
    } catch (e) {
      cardButton.disabled = false;
      displayPaymentResults('FAILURE');
      console.error(e.message);
    }
  }

  const cardButton = document.getElementById(
    'card-button'
  );
  cardButton.addEventListener('click', async function (event) {
    await handlePaymentMethodSubmission(event, card);
  });
});

The code does the following:

1. Binds the Card tokenization to the trigger event, which is clicking the Pay button in this case.
2. Submits the tokenized card information and payment token by calling the CreatePayment endpoint on the backend.

1. Navigate to http://localhost:3000/ in your browser.

2. Input the card number 5105 1051 0510 5100 from the Card-present success state values. Any CVV or postal code works.

3. Choose the Pay $1.00 button.

   

You should see a green check mark and Payment successful on the page. The payment is credited to your developer test account. The next section shows how to find the payment in the Sandbox Seller Dashboard.

Look at your Developer Dashboard for a debug log of the payment information.

The payment is credited to the Sandbox test account whose access token is used in the application that you just built. To see the payment in the Sandbox Seller Dashboard, go to the Developer Dashboard.

1. Choose Open on the default test account to access the Sandbox Seller Dashboard.

2. Choose Transactions.

   

You can see a complete code example in the Web Payments Quickstart in GitHub.

This section explains how to deploy your application in production with the following tasks:

• Replace your Sandbox access token and application ID with production values.
• Update your code to make API calls to Square production endpoints.

Deployment tasks include the following:

1. Get production application credentials - In the "Get Sandbox application credentials" section, you obtained Sandbox credentials. Follow the steps to open the Developer Dashboard, but this time choose Production mode and copy the production application ID and access token.
2. Update script references - In the ADD SCRIPT REFERENCES section, you added script references in index.html. Update the domain string in the JavaScript reference from sandbox.web.squarecdn.com/v1/square.js to web.squarecdn.com/v1/square.js.
3. Provide your production application ID - The Web Payments SDK requires a valid application ID to return a payment token. In the "Provide your application ID" section, you provided a Sandbox application ID. Update the code by providing your production application ID.
4. Configure your backend server to use a production access token - In the "Configure the quickstart access token" section, you provided a Sandbox access token in the env.sandbox file. Replace it with the production access token.

If you want to test the application in a production environment (squareup.com), you must use an actual payment card. Note that Square actually charges payment cards in production. Therefore, if you must test in production, charge minimum amounts.

Now that you're taking payments with credit and debit cards, you can add additional payment methods or customize the appearance of the Card payment method.

• Customize the Card Entry Form
• Add Apple Pay
• Add Google Pay
• Add ACH Bank Transfer
• Add a Square Gift Card
• Add Afterpay
• Add Cash App Pay

To add security to a payment method, you can add the 3D Secure security protocol layer to the application. 3D Secure integrates Strong Customer Authentication (SCA) to verify the identity of the payment card holder by using the verifyBuyer function.

• 3D Secure Overview

With card information, you can also save card information to file with the Cards API. For more information, see Cards API Overview.

The Web Payments SDK technical reference also provides a complete reference about supported payment methods, objects, enums, errors, and code examples.