I have an Iphone 6 and an imac 21 which show up in my itunes account as authorized machines. I have an Apple2 tv unithat is is always asking me to signin to my itunes account It alwsy says it cannot signin even thought i give it my Itunes/icloud inf

I have an Iphone 6 and an imac 21 which show up in my itunes account as authorized machines. I have an Apple2 tv unit (at a different location) that is is always asking me to signin to my itunes account It alwasy says it cannot signin even though i give it my Itunes/icloud password. I always recieve a message on my iphone thats asks if i will allow this or deny this request (i always allow). It also gives me a 6 digit security code. I dont have anywhere to submit that code on my Apple TV or it says something like enter the security code after the password. I have done this and it still says it can't login to my itunes account.