This is a mixed-content error.
A mixed content error essentially means that if the main web page begins with https://, all elements in the page (including any links or iframed forms) also need to begin with https://.
For example, if your landing page is set as https://go.company.com/free-trial and you have an image within the page that is linked to http://company.com/image, the overall page will not be secure. You would want to replace that image link with a link that begins with https:// to make the overall page secure.
To make the landing page secure, all links within the code of the page have to begin with https://.
Here's what to look for:
1. Look at the Layout Template the Landing Page is using and scan for any links that begin with http://.
2. Look for the <base ref> tag in your Layout Template. This could be pointing to a link that begins with http://.
3. Review any CSS (Cascading Style Sheets) and see if there are any http:// links in there.
Additional information:
1. Review this Knowledge Base article under "What considerations should I take into mind *before* enabling SSL for my tracker domain?"
2. Review this Trailblazer Community thread.
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