The second screenshot also says "Once you get to Six Paths Sennin Rank for the first time, you will not get any more rewards for advancing ranks since this is the highest rank"

It's a bad translaction but you need to hit six paths sennin rank first before you can earn the season rewards. Otherwise, you earn the rank of ninja school student. This has been brought up by several people in the past. Try to use their search function.

Oh okay, thanks for explaining :)