Why my xpcall yields but it should not yield?

( Sorry for being a bad post but this is my first post)

it always warns this: 18:12:12.104 - attempt to yield across metamethod/C-call boundary

the code:

local Succes,Error = xpcall(function()
           local _,Error3 = pcall(function()
           local ReservedServer = TeleportService:ReserveServer(tonumber(Level.GameNumbers.Value))
           TeleportService:TeleportToPrivateServer(tonumber(Level.GameNumbers.Value),ReservedServer,{player})
           end)
            if typeof(Error3) == 'string' then error(Error3) end
           end,function(Error2) 
                if Error2 == 'HTTP 403 (Forbidden)' then
                return "Cannot Teleport in Roblox Studio"
            else
                return Error2
            end end)
                if not Succes then warn(Error) end