Published by Marty Paukstys, founder of D2CEBL. 20+ years of Google PPC & Analytics experience. Google Ads Search and Google Analytics certified.
1/31/2025: The problem was Calendly's integration code was installed as an iFrame on your website. GTM could not be found, because it was not there. Your page was being tracked by GTM properly, but since Calendly's iFrame is "a page within a page", GTM tags were not there.
Since we have little, if any, control over iFrame's content and GTM code installation is impossible (or hard), it made sense to install Calendly's code differently. In this case, as a simple code directly into your website, not as an iFrame.
Now GTM is firing properly when in Preview mode, and events are being sent to your Analytics account.
GTM Preview Mode
Google Analytics Debug Mode
You can read more on Calendly event tracking with GA4 in our How-To section.