Developer Products not working on another game?

I very much no it's not the code, but I do know that it's not letting me make the Developer Product work on any other games. All it says in the game when I try to do this is Forbidden 403. I know it because it's in a different game. I am allowed to put my own developer products in the game, the owner said I could. So im not trying to do it in any shady way. I just want to make it work.

Heres the code, normally:

game.MarketplaceService:PromptProductPurchase(player, 944409237) 
local player = game.Players.LocalPlayer

this is inside of a GUI in a local script.

Thank you!