Unable to make in App purchases it says go to Apple support

Hello I am using an IPhone 6s Plus trying to make a in app purchase for a game but it will not allow me to do so. It did at first but now it doesn't . I thought maybe it was just the game app itself Acting up so I tried another game to check and see if I could purchase anything from that game and was still not able to. I checked the card info on the App Store and it was all correct except I have to keep putting the 3 digit security code in. Would like to have some help correcting this issue please. Thanks