When I submit my website rss feed (https://worldcup2018football.com/feed/) in alltop. They said rss feed is not valid. Still, I am visit the rss feed and I see rss feed is showing but, when I put the link in alltop they said rss feed is not a valid link
Have you tried contacting alltop’s support? If they say the feed isn’t valid, it’s most likely a problem on their end.
That said, your site, https://worldcup2018football.com/, is also not hosted with us, so we have no control over that site at all, including its feed. Your site is using the open source WordPress software found on WordPress.org, not WordPress.com. The two version of WordPress are completely separate and different.