I can't apply clothing to characters, can you help?

I have a mannequin stand to sell clothes on and I basically have it where you input the shirt id and pants id into a script and it automatically puts the clothes on the mannequin.

--PantsId
local Model = script.Parent
local Mannequin = Model.Mannequin

local PantsId = 382538503
local ShirtId = 1748598322

Mannequin.Pants.PantsTemplate = tostring(PantsId)
Mannequin.Shirt.ShirtTemplate = "http://www.roblox.com/asset/?id=" .. ShirtId - 1 -- HELP :(

-- Tried methods
-- Mannequin.Shirt.ShirtTemplate = "http://www.roblox.com/asset/?id=" .. ShirtId - 1
-- Mannequin.Shirt.ShirtTemplate = tostring(ShirtId)
-- Mannequin.Shirt.ShirtTemplate = ShirtId

--Prompts the player to purchase the items
Model.ShirtBuy.ClickDetector.MouseClick:connect(function(player)
    game:GetService("MarketplaceService"):PromptPurchase(player, ShirtId)
end)

Model.PantsBuy.ClickDetector.MouseClick:connect(function(player)
    game:GetService("MarketplaceService"):PromptPurchase(player, PantsId)
end)