My colleague is trying to preview some changes he made in our GTM account, however despite in the GTM interface the preview account is set as working, the preview panel is not loading on the website. We have tries everyting - different browsers, hard refresh, checking up pop-up settings etc, nothing is working.
Has anyone experienced the same thing?
If after trying the suggestions @stephen-ostermiller posted, you still can't load the GTM preview pane on the site- here are some additional things worth checking:
Open the site in a web browser and open/reveal the web inspector panel. In most browsers, you can right click on an element of the page and choose INSPECT ELEMENT. With the inspector open, navigate to the CONSOLE tab and see if there are any errors (you may need to reload the page). Ideally, the console will be clear or show only notifications/warnings (in white/yellow). Sometimes, javascript errors (denoted by a red X and highlighted in pink) can block subsequent javascript such as GTM from loading. Should you encounter javascript errors, consult your web developer.
Confirm that the GTM code snippets are in the html of the site/page in question. View the HTML source of the site and search for the code snippets containing www.googletagmanager.com/gtm.js and www.googletagmanager.com/ns.html. It should reveal your custom GTM code snippet, similar to the example posted on the GTM Quick Start Guide.
Having confirmed there are no Javascript errors and that the code is infact in place, make sure you are reloading the site/page with a hard refresh (thus bypassing cached content). This Tech Tip post lists the shortcut keys for most common browsers.
Also worth trying, sign into GTM on a different device and internet network to see if the preview pane still doesn't load. I've seen some internally hosted websites and networks block GTM preview.
If you just recently (within the last few hours) added GTM to your site and are trying to preview for the first time, make sure your website is not being cached at the server level- in which case, more than likely, you wouldn't see the GTM scripts being served to your browser, but do see it in the raw html on the webserver. If that's the case, you'll need to flush your webserver/varnish cache.
Adblock and Ghostery (or other plugins that are designed to block content) often cause this sort of problem.
That preview panel needs cookies to work. It sets a cookie that tells it to appear. Set your browsers cookie preferences to allow all cookies.
You need to set the preview on the same computer on which you are trying to view the preview. You can't set preview for your colleague and have them view it. They need to set preview themselves logged into GTM.
I'm suggesting these because we have the opposite question here: How do I hide the Google Tag Manager preview pane?. These are all problems people have encountered trying to get the preview panel to go away when they are done with it.
