For sources you accessed online, ideally your citations should include a link directly to that resource. However, often the URL you see at the top of your page when you are searching in a database is not a permanent link. That means that when someone tries to use that link in the future, they'll get an error message. When you are saving links to include in your citations, look for a stable or permanent link. Often a database will include a chain link icon where you can generate a permanent link.
You can also check if a link is stable by copying the link and pasting into an incognito browser window - if you get an error message, that means the link was not stable.