Well, regardless of the platform there are times you'll receive auto messages regarding missing information on your series or if you haven't been posting chapters for a long period of time (This one I tend to receive them from Webtoon, since in that platform you can mark a series as finished).
You don't necessarily have to open the links, you can simply go to your series's settings, see what are the requirements for the banner (size, format, etc) and done.