Therefore, the first thing you should check is whether the click variables are undefined, if you have thought about creating a click trigger. If the click variables are not defined, make sure you have selected the click event from the list of messages in the preview mode. One Click – All Items Triggers – if you want to track clicks on an item. A surprisingly common question in forums and communities seems to be why embedded click variables are shown as not defined in the preview mode by Google Tag Manager, even when the site is clicked. Of course, if you want to track clicks, you must create a trigger for all items or a trigger just for links, since both clicks click on the track. You MUST create a trigger so that the click variables can be filled with values. At this point, each click on your web page must insert a click element in the Preview Mode window. This is not relevant if you want to know what values were present when a tag was launched, for example, because you need to select the triggering event for the tag to know. If dataLayer is corrupted, no event with name debugging is shown in the preview mode message list. The GTM preview mode shows the values of the variables that existed at the time the selected message was processed. However, if the GTM container manages to load before it is overwritten, you can still see the Page View event, even if it is missing in the data layer. So it’s a chic and eggy situation – you can’t create the detonator until you know what to follow, and you can’t continue until you create the detonator. A form send trigger – if you want to track the sending of a form element. It is only by creating the trigger that the GTM begins to hear the click events.