Some "generators" are actually front-ends for databases of previously leaked or publicly shared codes (from pastebin, cracked forums, etc.). They aren't generating anything; they are regurgitating old, often expired, credentials. By the time you see them, the codes are almost always dead.
Free Xtream code generators claim to provide daily working credentials (URL, username, and password) that allow users to access live TV and VOD content via IPTV players like IPTV Smarters Pro or TiviMate . Xtream Code Generator - Apps on Google Play xtream code generator free