A connection could not be established

 Hello. I'm new to TeamViewer.  I just downloaded TeamViewer and registered my account. The green light is indicating that I'm online. My client installed quick connect and she is online. when I enter her partner id I get an error message (a connection could not be established) any ideas what could cause this. We're both online and the software is running.  I'm a mac running is latest OS and she on a windows 10 latest version