HTTP 403 (Forbidden) How to fix that?

You're using game.Id wich doesn't exist, you have to use PlaceId So instead of game.Id use game.PlaceId Also, the third argument for :TeleportToPrivateServer() must be a table, not a player.

So you have to do this

local Id = "000000000" -- Don't mind there's should be real Id

local TeleportService = game:GetService("TeleportService")

local Trigger = game.Workspace.TeleportTriggerLeft

Players = game:GetService("Players")

Trigger.Touched:Connect(function(trigger)

    local character = trigger.Parent

    local player = Players:GetPlayerFromCharacter(character)

    print(player.Name.. " Touched the trigger!")

    local Reserve = TeleportService:ReserveServer(game.PlaceId)

    TeleportService:TeleportToPrivateServer(game.PlaceId, Reserve, {player})

end)

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