Transparency rendering for After Effects Not Working??

Hellow All , i am very new at this , following tutorials , i managed to get all working ( i am tracking camera in AE , so i can add my models in UE, But when i export the model after, the background still shows even if i untick them in “view” . This is a link with a short video explaining. Thank you all https://www.youtube.com/watch?v=HRuTT8FFxX8