Error with w3c validator

Hello,
I was using the validator https://validator.w3.org/ to test my homepage.
I see the error in attachment related to the plugin.
Anyone knows how to solve?
Thanks
https://ibb.co/Xj2WScw

• This topic was modified 4 years, 4 months ago by ita10.
• This topic was modified 4 years, 4 months ago by ita10.