The most common accent error patterns for initial Z /z/ are devoicing (sounds like "s" /s/) or stopping with affrication (sounds like "j" /dʒ/). Make sure your voice is on and the sound continues. There are not many commonly used words that start with z in English, so additional words are included in the practice recordings. Try to notice whether you frequently use any initial Z words (for example, do you have a zero in your address or phone number? Do you need to say "zone" or "zip code" at work?). If so, practice the context in which you need to say initial z.