How do I give out swords after purchasing a dev product?

When you want to prompt the purchase of a developer product, run this (replacing the player with path to the player and productid with the ID of the product.)

game:GetService("MarketplaceService"):PromptProductPurchase(player, productId)

Then put this in a script to actually give out the swords.

local devId = 0 --Put the dev product ID here
local sword = game:GetService("ServerStorage"):FindFirstChild("Sword") --Put the path to the sword here

game:GetService("MarketplaceService").ProcessReceipt = function(receiptInfo)
    for i,v in ipairs (game.Players:GetChildren()) do
        if v.userId == receiptInfo.PlayerId then --If the player matches the player in the receipt
            if receiptInfo.ProductId == devId then --If it's the correct developer product
                if pcall(function()
                sword:Clone().Parent = v.StarterGear
                sword:Clone().Parent = v.Backpack
                end) then return Enum.ProductPurchaseDecision.PurchaseGranted end --Tells the marketplace service that purchase went smoothly.
            end
        end
    end
end