[操作系统]解决 an app id with identifier is not available. please enter a different string. xcode 7.3
百度上这帮人，真的服了，没有一个人能解决问题，最后在 stackoverflow 上找到解决方法
The Application ID Name should be same as application bundle identifier, if you application bundle identifier is com.abc.xyz than the application ID name for this bundle ID should be XC com abc xyz
A name in any other format won't be seen by Xcode.
If you your application is already on app store and you are submitting update than just change the app ID name accourding to above formate and it will work