Rome and Barcelona scored the same score. Why did Barcelona get eliminated?

20 17- 18 Champions League season, Barcelona and Rome met in the final of14. The first leg of the two teams was held in Camp Nou, and Barcelona won by 4:/kloc-0. Everyone thought that Barcelona would definitely advance. In the second round of Rome's home game, Rome unexpectedly beat Barcelona 3-0, and the total score of the two teams was 4-4. However, because Rome scored an away goal at home in Barcelona, it has the advantage of comparing away goals with the same total score; With Rome's precious away goal advantage, Duoyi finally eliminated Barcelona and entered the semi-finals of the Champions League:)