<link>
To add Web Monetization to your page, you will need to add a <link> tag with a rel='monetization' indicating that some content on the page is monetized.  While an HTML document can contain unlimited monetized <link> tags, implementations may restrict how many of those links are actually monetized. 
Examples
<link rel="monetization" href="https://example.com/pay">
Monetization load events
<link rel="monetization" href="https://example.com/pay">
<script>
  const link = document.querySelector('link[rel="monetization"]');
  link.addEventListener("monetization", event => {
    // See how much your received and in what currency
    const { amount, assetCode, assetScale } = event;
    console.log(`Received ${assetCode}${amount} (${assetScale}).`);
  });
</script>