What does - '(Username) may not be contacted at this time' mean?

I was working back and forth with a buyer on some revisions. Fiverr ended up marking the order as complete. I went to go message the buyer and received the message '(Username) may not be contacted at this time'. I thought maybe the person deactivated their account or something so I figured I would check back in the morning and see. Except I just received a message from them. I don't understand. I don't want them to give me a negative review because they think I'm ignoring them, but I'm not sure what to do.

Any helpful tips?