If the prayer of the congregant (ma'mum) is invalid, does the imam still receive the reward for the congregational prayer?

The prayer of the Imam is not invalidated by the invalidation of the prayer of the congregant; the Imam's prayer remains valid.

As for whether the Imam attains the virtue of congregational prayer in the event that the congregant's prayer is invalidated, there are two views: 1. The Imam is not required to repeat the prayer in another congregation. 2. The Imam should repeat his prayer in a congregation, while some scholars refrained from giving a definitive opinion.