We need all of your code please.
Just copying the error message is better, but not great. Its polite and helpful if you put forth as much effort into asking the question as you want me to put into answering the question.
I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).
The problem, quite literally, is that you don’t have an footer element with the id tag of "footer".