iCloud password verification fails despite correct credentials on iPhone

tired of seeing pop up screen for icloud, always asks for password and i definately give correct password but it always says verification failed, can log into apple account no problem, even did the forgot password thing and made entirely new one and it still does the same stupid thing

[Re-Titled by Moderator]

Original Title: i can log into account, but then a icloud pop up box appears on screen, asks for password and always says failed