I did a forzathon and havent received the Merc C63 Fe what can I do

try reading some of the 50 or so threads on that exact same issue in the fm 7 SUPPORT forum

Well done mods
Moved to suppprt

I did not receive it either. The challenge shows up as complete.

If you are showing completed. Try hitting Xbox button, go to network settings, go offline, wait a few seconds, go online. Wait for service status, hit b button until back in game and check your car collection menu to see if it’s showing you own the car, if it shows as owned, check garage. Go to forzathon menu after.

i tried the settings route but it didn’t seem to work. I tried to get the dodge dart forza edition but it kept saying the forza servers weren’t available and then tried giving me the car and after a while it said it was complete without giving me the car.