I hear the audio says: "daftar". If we write the Harakaat completely, it is "daftar(un)". دَفْتَرٌ. The -un sound is nothing to do with whether there is ta marbuTa or not. But, it is because of the case. In the nominative case, "daftar" is pronounced as "daftar(un)".
In the daily conversation, people often omit the ending sound and say "daftar". However, formally we can say "daftar(un)".