Hi Oleksii,
Welcome to Responsive menu Pro Support Forum. Hope you are having a great day.
May be these 2 plugins aren’t compatible with each other. That’s why the shortcode isn’t working in the Additional content area.
If you want to show social media icons on the menu.
The easier way to do this is, just download the social media icons from the Internet and upload them to the media library of your website.
Then copy the URL of that image.
Now, paste the following source code in the ‘Additional Content’ section of the container.
<a href="https://www.facebook.com/">
<img src="http://localhost/responsivepro/wordpress/wp-content/uploads/2019/12/download.png" width="40" height="40">
</a>
You need to replace the ‘href’ value with the URL of your fb fan page and also replace the ‘src’ value of the image with the URL of the image you copied above.
You will have to do this for every social media icon.
Hope this helps to resolve your query.
Regards,
Kriti
.