Use the address in the email
The welcome email includes a web address as well as the television player. Open that address in Chrome, Edge, Safari, or Firefox. Sign in with the same username and password. Do not search the web for a random player page. Other sites are not IPTV Moon.
Leave the tab in the foreground. Browsers pause video in background tabs, which looks like buffering. A laptop on Wi-Fi has the same needs as a television: a steady connection, and a free screen on your plan.
When the browser is the wrong tool
The living-room television is still the better screen for a full match. Use the browser for a desk or a hotel. Setup for the television is in Smart TV setup and Fire TV and Android TV.