You shouldn’t be trying to learn grammar through WaniKani. You will be much better off learning through outside sources. You can check this thread for a full list of recommended resources by the community. Personally I’m mostly learning grammar through Genki, Bunpro, and a small bit of Tae Kim.
EDIT: Just to add a bit more clarification, the entire point of WaniKani is to focus on kanji. By not trying to also teach in grammar it is able to excel more so in that category.