It says it's currently under repair, I believe? Which means they're focusing in fixing something :)
Maybe
Many people have had the same pop up on it when trying to add to lists so I do think it's due to site lag and list issues that they've paused it. In the meantime you can bookmark any new manga, or copy their links to a Google document / phone notepad for safe keeping
It's a glitch or a bug mods are fixing it
Why dose it tell me it is “currently unavailable when I want or add a new manhwa or manga ??