I'll start with I play on PC and I don't use any mods. I started a new character for the event, a single female living in Willow Creek. I was able to do the event through the planting of the flowers ...
Ideas
I had the same problem in the game on my PS4. So I started a second game. I built a basic sim and housed them. I then saved them to a new game instead of saving over my original game. Waited a few days and got the mail. It worked and gave the credit/points. I saved the game and went back to my original game, it still showed as counted for. Though you got to go out of your way and create a second game, it does fix the issue and work.