I am trying to test for seasonality of the time series using Kruskal-Wallis test. My data is in the form of months and spans over 3 years. i want to do a quarterly analysis specifically oct-dec of every year.

This is the code i used:

p<-ts(data=data$rupee, frequency = 12)
q<-aggregate(p, nfrequency=4)

I got a p-value>0.05. However, my plot seems to indicate indicate seasonality:
Decomposed ts

Please let me know what I’m doing wrong.