UPDATE : After tried packaging and downloaded from iTunesConnect, still failed at the IAP. So the scenario i tried now is in DefaultEngine.ini there’s no added lines( since i added those codes doesn’t work as well and showed 2 log lines which OnlineSubsystemiOS cannot be loaded even plugin is enabled), copied iOSEngine.ini from Engine to project folder(As shown in documentation), packaging is set to shipping and distribution, using all distrubution provision and cert, not working at last! ShowExternalLoginUI works at Main Screen by login GameCenter.**