I had a similar problem when I first tried downloading the game. I think it means there isn't enough storage space for the game to be downloaded? Of course, I'm not very good at reading japanese, so it could mean something else entirely. Try clearing out some space on your phone and see if that works!

Hi! it could mean that it was on maintenance, if you logged on today it should be fine maybe? if you see something along that says メンテナンス (maintenance) it should be it. or if there's a button that leads to appstore it should need an update. if it still has a problem, feel free to send a screenshot

I had the same problem! Mine was downloading very slowly and it turned out that my router was too old, so I suggest checking if your router has any problems. The pop-up thing basically is telling you that connection was lost during the download, which typically happens when your wifi is weak. All you need to do is click the pink button and it will continue downloading from where you left off!