Thanks for the feedback, but Perspective is to keep the community clean of toxic language even from long term members (in particular in our community, new members are mostly friendly 
).
And as the popup comes up, the call to the API seems to work on edit, but just the flagging is not happening. Maybe the plugin can check if the same post has been flagged before already (for whatever reason), and if so don’t flag again, but changing a harmless post into something toxic (without being flagged before) should be flagged. Our long terms members will fast figure out this loophole.