By default, Joomla content plugins will always work inside articles

However, they may often not work inside Custom HTML modules, even though those modules also have a WYSWIYG editor.

In this short tutorial, we will show you how to enable content plugins within your Custom HTML modules. 

• Go to Extensions > Modules > New > Custom HTML (or Edit an existing module).
• Use your plugin. In my example, I’m using OSYouTube plugin. I add the URL of a YouTube video inside the text area of the module. If the plugin is working correctly, the link should be converted to a video.

Now let's enable the setting that makes it possible to render plugins inside our modules:

• Go to the Options tab.
• Set Prepare content to "Yes".

• Click "Save and Close".
• Preview the module on the front-end to confirm the plugin is working inside the module.