Jan BM3,795 Points
How come that this appeared in my theme checker and how to resolve it?
"REQUIRED: Sidebars need to be registered in a custom function hooked to the widgets_init action. See: register_sidebar()."
I've been following your video but I can't seem to find that it triggered to you.
With errors like that, it is always best to refer back to the Wordpress codex, and ensure that you are using the proper code to create and call your sidebar. In this case, it looks like the error stems from your functions.php files where you should create your sidebars.
I hope this helps.