Polar を接続し、注文を訪問に紐づける

// Express with cookie-parser, where you create the Polar checkout.
app.post('/checkout', async (req, res) => {
  const visitorId = req.cookies['_tally_vid'];
  const response = await fetch('https://api.polar.sh/v1/checkouts/', {
    method: 'POST',
    headers: {
      Authorization: 'Bearer ' + process.env.POLAR_ACCESS_TOKEN,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      products: ['your-product-id'],
      metadata: visitorId ? { 'tally_visitor_id': visitorId } : {},
      success_url: 'https://example.com/thanks?checkout_id={CHECKOUT_ID}',
    }),
  });
  const checkout = await response.json();
  res.redirect(303, checkout.url);
});

// On pages with Polar checkout links: add the visitor id as reference_id. Polar's embed
// marks its links with data-polar-checkout; use your own selector for plain links.
const visitorId = (document.cookie.match(/(?:^|; )_tally_vid=([\w-]+)/) || [])[1];
for (const link of document.querySelectorAll('a[data-polar-checkout]')) {
  const url = new URL(link.href);
  if (visitorId && !url.searchParams.has('reference_id')) {
    url.searchParams.set('reference_id', visitorId);
    link.href = url.href;
  }
}