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