A talked about the order, but the customer didn't talk to A, and B talked about the order successfully. How should I calculate the commission?

A of B is the initial contact of the customer, that is, the customer initially contacted A and expressed the purchase intention, but A was unable to follow up for some reason, and then B took over and finally completed the sale, so the commission will generally be given to B, because B continued to provide services after A and reached the sale.