Implement Recurly.js to tokenize card data client-side and use the token to create a Recurly subscription without handling raw card data server-side

Steps

1. Include Recurly.js on the page: <script src='https://js.recurly.com/v4/recurly.js'></script> and initialize with recurly.configure({ publicKey: 'YOUR_PUBLIC_KEY' })
2. Mount the card element: recurly.Elements() to create a CardElement and call cardElement.attach('#card-element') to render a hosted card input iframe
3. On form submit, call recurly.token(form, (err, token) => {}) passing the form element; Recurly returns a single-use token string
4. Submit the token to your server and create the billing info with PUT /sites/SITE_ID/accounts/ACCOUNT_CODE/billing_info using token_id: TOKEN_VALUE in the request body
5. Create the subscription server-side with POST /sites/SITE_ID/subscriptions providing account.code and plan_code — Recurly retrieves the stored billing info automatically
6. Handle tokenization errors in the client-side callback; error.fields array lists which card fields failed validation (number, month, year, cvv)