You'll need to get first place in all career events, including promotion events, but not vehicle challenges. Make sure to get first place in all the events before you move to the next season, and if you are struggling, make sure to remember that you can change the difficulty to very easy if necessary.
Warning: If by any case you forgot to complete some promotion event during the storyline there's a problem, when you complete a promotion event while playing the storyline they will be marked with a green mark, if you choose them by the timeline and you complete you'll notice that they wont be marked with the green mark but its still possible to get the achievement as i've done this way, just take note of any event you complete and they will count.
Update: Briana11 VR46 said after the last update the green mark is appearing, i didnt check but if thats true there's nothing more to worry about.
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