Just popping in here as this is something that I had a lot of trouble with too, and honestly would have probably killed wanikani for me if I couldn’t fix it. I got so caught up wondering if what I was about to enter was going to be marked wrong for invalid reasons that I just didn’t want to do my reviews at all, and that would have been such a waste, as wanikani is an absolutely fantastic learning platform.
What I did was install this great userscript: [Userscript]: Double-Check (Version 2.x), which lets you submit an answer without it being final, so if you are marked wrong but you’ve just made a spelling mistake (or entered a reading for a meaning, etc) you can correct it and move on. This and a number of other scripts (many developed by rfindley, just like this one :P) have made wanikani absolutely amazing, so I’d highly recommend it if you’re in the same boat. Just make sure not to abuse it - mark things wrong if you get them wrong, otherwise you won’t get to review them again properly!