Each element with the class of “main-section” should also have an id comprised of the innerText contained within it, with underscores in place of spaces. The id may include special characters if there are special characters in the respective innerText. (e.g. The that contains the header, “JavaScript & Java”, should have a corresponding id=“JavaScript_&_Java”).
I think you have to either remove the & from the href or add the & to the id, so both href and id have the same name. Your section id name is “Mers_Covid-19” but you are telling your link to go to Mers_&_Covid-19 which doesn’t exist.