I have this exact same problem. Doesn't matter if you say OK or Cancel or try manual homologation. No matter what you do it won't let you use the car, But the car is completely stock and matches the requirements. I have an XBOX ONE.
Originally Posted by: GeoBem007 
Hi,
I have encountered a bug recently with FM7 on my Xbox One S.
I was entering the Formula E Championship in the Breaker Championship. The Formula E is the ABT-Schaeffler one that I had chosen as level up reward.
When starting the race, the game gives me a pop-up saying I need to homologate my car to be able to enter the race.
I had changed the wheels. The PI had not changed, as I fitted a wheel with same spec as the stock wheels.
Anyway, pressing OK to homologate the car, the game says it needs to homologate automatically. Pressing OK again, the pop-up dissappears and I can start race. But I can't. Because when I click again to start the race, I get the same message.
When changing the wheels back to normal, I get the same pop up and after the homologation is done I get the message that the car is homologated for the event. But again, when wanting to start the race I get the pop up again.
Xbox has been rebooted and the error stays the same.
Anyone with a similar issue? I have not yet tried buying another Formula E car as they are not cheap and the way FM7 now values cars, I'm keen on keeping my credits as much as possible.
Oh yeah, the game mentions that I have one eligable car in my garage for the cup so it recognizes it for real ;-)
Thanks!
Kind regards,