Warning: enabling HTTPS in the Joomla control panel is no longer possible to open the page for entering coordinate in ContentMap parameter in the individual articles.

ContentMap uses the external service mygeoposition.com to manage the page where you define the coordinates to be included in the article. This service is not yet available in HTTPS and therefore does not appear if you open a page in HTTPS, so it works properly only if the Joomla control panel is in http .
Alternatively, you can manually enter the value of the individual coordinates point in the article, pasting the value in this way: 28.728573, -13.867734

You can obtain the value of the position to copy and paste in the ContentMap parameter from mygeoposition.com site or from Google Maps doing with the right mouse button on the desired location and selecting "What's in here?".

The behaviour of the maps, both the module or of the individual articles, continues to function properly even in HTTPS, only the page to derive the coordinates is no longer visible.