ive tried to connect my Apple TV to my Optus NBN wifi but it won’t work. Apparently sometimes you need to validate the WIFI to allow access to connect it to Apple TV. Anybody know how to do this?
Not sure of your actual situation - Apple TV3 is 2.4Ghz linked and Apple TV4 supports 2.4Ghz and 5 Ghz - are you connected successfully to the respective Wi-Fi radio of the Modem? If that is OK, from memory, to make the Apple TV a recognised device in your Apple Account Profile, you need to establish or log into your Apple iCloud Account through the Settings Icon of the Apple TV to register it with Apple. During this process, you should be presented with a Two Factor Authentication (TFA) code on your Mobile or EMail account to verify it is you and enter this into your Apple TV screen when asked and you should be good to go.
Your iCloud account is also used for identification and billing purposes if you use the Apple billing function of streaming Apps through the Apple TV. These Apps can also have an alternative direct billing arrangements with companies through your normal email ID and password and when you click their Icon, they will request you to verify your specific User ID and Password that you established for them - I would expect TFA to apply with them as well. I have no experience with the Apple TV4, so not sure if the specific problem you have had to date relates to its registration with Apple - it may be different in the Apple TV4.