Shop / Purchase Flow

Server-authoritative | validates stock and currency, deducts, then pushes the inventory update reliably.

copyapp:Get("shop/catalogue", function(Player, Payload, req, res)
    res:Send(catalogue)
end)

app:Get("shop/balance/:userId=number", function(Player, Payload, req, res)
    res:Send({ balance = currency[req.params.userId] or 0 })
end)

app:Post("shop/buy", function(Player, Payload, req, res)
    local item = catalogue[req.data and req.data.itemId]
    if not item                               then res:Status(404):Error("Not found");      return end
    if item.stock <= 0                         then res:Status(400):Error("Out of stock");   return end
    if (currency[Player.UserId] or 0) < item.price then res:Status(400):Error("Insufficient funds"); return end
    currency[Player.UserId] -= item.price; item.stock -= 1
    app:Push(Player, "shop.purchased", { item = req.data.itemId, balance = currency[Player.UserId] })
    res:Send({ success = true })
end)

See also

App  ·  Server Push  ·  Router | typed param :userId=number  ·  MVC Pattern | refactoring this into clean architecture  ·  Inventory System | full CRUD with DataStore