"Como vai" is a better translation for "What's up" since both of them are commonly used in a informal way.

The “está tudo certo?” expression is not very common in Brazilian Portuguese in this context. A more appropriate one would be “o que houve?”, as in, “did something happen/what is it?” but more polite than “o que foi?”

There are two sentences in the text. Therefore, there must be a "period" to start a new sentence. The use of a comma is incorrect in this case. And when the program is asking What's up, the intention is to know if something happened on the other line and the translation for it is "O que aconteceu".