LemonSqueezy Checkout API

Pass the Talivia session when your backend creates a custom LemonSqueezy checkout.

Use this flow when your backend calls POST /v1/checkouts and returns the generated checkout URL to the browser.

Send the session to your backend

Read the current session on the tracked page and include it in your own checkout request:

Start checkout from the browser

const sessionId = window.talivia.getSessionId();

const response = await fetch('/api/create-checkout', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ sessionId }),
});

const { checkoutUrl } = await response.json();
window.location.assign(checkoutUrl);

Treat the session ID only as attribution context. Validate the customer, product, price, and authorization independently on your backend.

Add custom checkout data

Merge the received value into attributes.checkout_data.custom in the LemonSqueezy request:

Create the LemonSqueezy checkout

const checkout = await fetch('https://api.lemonsqueezy.com/v1/checkouts', {
  method: 'POST',
  headers: {
    Accept: 'application/vnd.api+json',
    'Content-Type': 'application/vnd.api+json',
    Authorization: `Bearer ${process.env.LEMONSQUEEZY_API_KEY}`,
  },
  body: JSON.stringify({
    data: {
      type: 'checkouts',
      attributes: {
        checkout_data: {
          custom: {
            talivia_session_id: sessionId,
          },
        },
      },
      relationships: {
        store: { data: { type: 'stores', id: process.env.LEMONSQUEEZY_STORE_ID } },
        variant: { data: { type: 'variants', id: variantId } },
      },
    },
  }),
}).then(response => response.json());

return Response.json({ checkoutUrl: checkout.data.attributes.url });

LemonSqueezy copies custom checkout data to meta.custom_data in the signed webhook. This works for hosted custom checkouts and programmatically opened overlays.

Keep the LemonSqueezy API key on the server and preserve any other custom fields your application already sends.