Some Irisalis players have been confused about the Petal rewards connected to the Aniimo Topic section. The objective can appear to point toward the Anidex, but the actual progress is tied to completing specific research tasks and discovering the required Prismana forms.
This is one of those event mechanics that is easy to overlook if you only check the main reward screen.
Before assuming a Petal reward is bugged or unavailable, check your Aniilog and research progress. Missing forms may be the reason a reward has not unlocked yet.
This https://www.mmoexp.com/News/aniimo-iris ... rency.html covers the different ways to work toward the Petal total.