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Forzathon" is on the Main Menu & the pre-race menu.
Clean Sweep is 1 of the 3 events.
Each Forzathon event has 3 parts: Challenge 1, 2, & 3.
For Challenge 1 "Beat a Rival" go to "Rivals".
I completed the rest in
Forza Driver's Cup.
Free Play only worked for 1 of the challenges, so I found Driver's Cup events that matched the car division requirement of the challenge.
For a specific track requirement, I did Driver's Cup races until the correct track showed up.
Muliplayer is supposed to work also but the lobby kept dropping me.
From the Help screen in the Forzathon list of challenges:
"After completing a challenge & earning a Forzathon reward in Multiplayer, return to the Forzathon screen from the Pre-Race Menu or the Main Menu to claim the reward."UPDATE: Free Play should work now.
from ForzaMotorsport.net - "Also, note that we are aware of some known issues with the current Forzathon events, including the progress bars in the #Forzathon screen not reflecting progress right away [UPDATED 6:48 p.m. – This issue has been resolved. The “Welcome to Forza Motorsport 7” #Forzathon event should now track and complete as intended]. The team is currently investigating now. In the meantime, check out our Known Issues thread on the forums for the full rundown."
https://www.forzamotorsport.net/en-us/news/wir_11_10_17