@pameez Are you getting an error when sending the invite? What happens when you attempt it?

The option to send is not populating, see below. This appears to be only for one client.

@pameez Thanks for the screenshot! 
When you enter the email address, does the button highlight for you? Thanks! 

No it doesn't.

@pameez Thank you so much for confirming. This is not typical behavior and we'd definitely like to look at things more on the backend, if you wouldn't mind giving us a call to support. Based on the fact that it's just the one client, we suspect this will need a more in depth approach. Thanks!