Roblox doesn't let you send Robux to another player directly - the common workaround is having them create a gamepass and buying it from them yourself. Since Roblox takes its marketplace fee out of the sale first, the price has to be set higher than what you actually want them to receive. Enter the amount you want them to net and this works out the price to tell them to charge. Defaults reflect the commonly cited 30% marketplace fee, editable in case Roblox changes it.