I can't log into the App Store oh my phone, but I can log into iCloud in the setting with the same account!
I have 2 App Store accounts, account #1 and account #2
I can't log into the App Store to update the apps on my phone, but I can log into iCloud in the setting with account #1! I can also log into the iTunes on my computer.
When I try to log into the App Store with account #1, it will popup and say "verification failed. You Apple ID or password is incorrect." even though I am using the correct ID and password! because I am logged into iCloud with account #1!!
FYI: I have no trouble loging into the App Store using account #2.
iPhone 6 Plus, iOS 9.0.2