This is a virtual currency, which is not tangible, and Sayed Sistani says that dealing with it is not permissible based on obligatory precaution. As per the answer from Sayed Sistani's son, selling the said currency is not allowed, based on obligatory precaution, in which you can refer to another scholar who allows so. You can refer to Sayed Mohammad Saeed Al-Hakeem, and sell them.