Pokemon GO shop white screen is a rather annoying bug affecting Pokemon GO players.
The white screen glitch is a known entity in Pokemon GO. Some variation of unresponsive or blank screen seems to rear its ugly head every time the app updates. The newest glitch specifically targets purchasing tickets in the in-game shop. The glitch manifests when a player attempts to buy an event ticket. Instead of being taken to a purchase screen, the player is greeted with a blank white screen. This is especially annoying with GO Fest on the horizon since its ticket is one of the ones that could be locked behind the white screen.
Pokemon GO Shop White Screen: What it is and How to Fix it
First, if you have an Android, try clearing the data cache of the app and restarting it. You should be able to find this in the app settings. If the shop is still broken when you restart the application, it's time for the nuclear option. Your second and final option is to uninstall and re-download the app. This should fix the problem for you but you also risk losing your data if you can't remember your login info. So before you do this, make sure you have all your account information handy.