What is the ruling on drinking or selling Pepsi?

The basic principle concerning substances is permissibility until evidence of their prohibition is presented, based on the Almighty's saying: "And He has already explained to you what He has forbidden to you." The absence of evidence for prohibition is evidence that it is not forbidden. Whoever claims that something is not permissible to consume is required to provide proof for that. There is no reason that inherently prohibits the consumption of Pepsi.