Check the snippet
Copy the current snippet from https://app.message.com/settings/chats/installation. The script needs the correct data-site-id value. Install it once on the published site, not only in the builder’s preview.
Check the network
Open your browser’s developer tools and reload. Confirm that widget.js loads and that the widget can connect to its configured server. Test in a clean browser session to distinguish a browser extension block from a site configuration problem.
Check visibility and hours
Review widget customization, availability and office-hours settings. A hidden or offline widget can be a configuration choice rather than a failed installation.
Check your site policy
Look for Content Security Policy errors in the browser console. Allow the script, connection and media origins actually used by your installation. If it still fails, send support your public page URL, browser version and the error text, without including credentials.
Keep going
Put the next step into practice, or ask us about your setup.