You need to start the game with steam. Sadly, if you buy one DLC on steam you have only access if you start it with steam. I would not recommend mixing EA app and steam for sims 4 DLC. If it possibly I would try to get a refund on steam and buy it again on EA app. Steam normally give you without issue a refund.
When I try to start it in steam, first it plays a video of the content, then when I try play now, it tries to open through ea app, which has been coming up with an error stating there's an error on their end, try a little later. I've now requested a refund with steam. I have learned my lesson when it comes to trying to get a bundle cheaper
