html - iframe blocked as insecure content, even though the iframe is HTTPS -

i trying embed iframe (containing shellinabox, if that's relevant) onto https webpage. html i'm using embed iframe pretty straightforward:

<div class="jumbotron" style="min-height: 400px;">      <iframe src="https://example.com/shellinabox" style="border:none; min-height: 400px;" width="100%"></iframe> </div> 

however, chrome blocks iframe loading because "insecure content," , have manually unblock work. chrome console reports error this:

mixed content: page @ 'https://example.com/mainpage/' loaded on https, requested insecure resource 'http://example.com/shellinabox/'. request has been blocked; content must served on https. 

i confused because html code embedding https version of example.com/shellinabox. moreover, when visit https://example.com/shellinabox directly, lock icon green, nothing blocked, , there no indications of ssl problems on page.

i tested in firefox, ie, , ms edge, , have same behavior (so it's not chrome-specific issue). gives?

your code loading page on https page trying load additional scripts or assets on http. or may have scripts in page making ajax requests on http. youll have examine page , in developer console see insecure requests are. it's not issue how creating iframe element.