Can't Invite Partner

I've used Teamviewer for a very long time and it is a great tool. I recently tried to invite a partner so I could help them on their computer but instaed of creating an email, it just opened a browser and wanted to take me to the Teamviewer web site. Has something happened to this feature?  Second note, the person I want to invite has a Mac, and I have a PC. This combination does work?