I answered with "Chúng tôi tin vào tổng thống của chúng tôi" and was marked wrong, where the anwer mandated tin vị. So just wanted to check if "tin vào" was also acceptable or not.
Using "tin vào" is totally normal and should be accepted.
"Tin vị" is not a word, but it is "tin vị Tổng thống", in which "vị" can be considered as a (formal) classifier for human.
I said just "tin tổng thống" without vào or vị. That seemed to be the answer it wanted.