Install a compatible player from the tvOS App Store, sign in with your Xtream Codes details, done. The iPhone keyboard trick makes it painless.
On the Apple TV, open the App Store and install a compatible IPTV player (e.g. IBO Player).
Launch the app and accept the terms of use when prompted.
Choose the Xtream Codes API login (or “Add playlist” for your M3U link).
Enter the Server URL, Username and Password from your welcome email. When the text field is active, your iPhone pops up a keyboard notification — typing there is far quicker than the remote.
Confirm and let the app load your channels and guide; the first sync can take a minute.
Open Live TV, Movies or Series and press play.
Check the Server URL, Username and Password character by character — tvOS text entry makes typos easy. Use the iPhone keyboard prompt and copy-paste from your welcome email.
Plug into Ethernet if you can, or move to 5 GHz Wi-Fi. Restart the Apple TV (Settings → System → Restart) to clear memory before a long viewing session.
Search the tvOS App Store for “IPTV player” and pick one that supports Xtream Codes or M3U. If yours misbehaves, IBO Player is a reliable choice — your login works in any compatible app.