How can I input a stock with $0 cost?
Is it a share reinvestment program where you gave up on the dividends? If so, I would still say the cost is the dividends that you would have gotten otherwise?
Is it a bonus shares? If so, I would just create a buy transaction with cost = 0.
Is it a free shares that you have never owned? If so, I would still try to assign a “cost” to it. What “price” did you have to pay to get this “free” stock? It is because for new stock that does not exists in your portfolio, if you put the buy price to be 0, some computations will be NA.