The most common cause is the AddEvent JavaScript snippet not loading correctly on your page. Check that first before investigating anything else - it accounts for the majority of cases.

Checklist in order of likelihood

1. JavaScript snippet not loading Open your browser's developer tools (F12 → Console tab) and look for errors mentioning addevent.com. The snippet must be present on the page for the button to render. If you added it to a template header/footer, check that the page is actually using that template.

2. Conflicting scripts or ad blockers Test in a private/incognito window with all extensions disabled. If the button appears in incognito but not normally, a browser extension (ad blocker, privacy tool) is the cause. uBlock Origin and Privacy Badger commonly block third-party calendar scripts.

3. Content Security Policy (CSP) headers If your site sends strict CSP headers, they may be blocking the AddEvent script from loading. Check your browser console for CSP errors mentioning addevent.com. Whitelist *.addevent.com as an allowed script and connect-src source.

4. Dynamic/JavaScript-rendered pages If your page loads content asynchronously (React, Vue, Next.js, etc.), the AddEvent script may initialize before your button HTML is in the DOM. Ensure the AddEvent script loads after the button element is rendered, or call the AddEvent initialization function manually after your page mounts.

5. Plan limit reached If your Add to Calendar clicks are exhausted for the current usage period, buttons stop rendering. Check your usage in the AddEvent dashboard.

6. Hard browser cache Try Ctrl+Shift+R (Windows) or Cmd+Shift+R (Mac) to force a full page reload without cache.

If none of the above resolves it, contact AddEvent support with the page URL and a description of what you see in the browser console.