Is one who works for a company that develops a social media application, which may be used for either the forbidden or the permissible, sinful, and is his money unlawful, knowing that one of the managers is considering using it for forbidden matters while he intends to use it for permissible matters?

The permissible programs, their fundamental principle in operation, is permissibility. There is no harm in developing the aforementioned program merely based on the suspicion that some people will use it for illicit purposes. However, the developer is sinful if it is highly probable in his estimation that the majority of people will use it for illicit purposes.