When a call request is made, both member and expert will have the capabilities of sending each other messages.
To send a message, go to your Calls page > Select the member/expert you'd like to send a message to > Click "Send a Message".
You send a message to experts to ask clarifying questions before requesting a call by going to their profile, and clicking on the little envelope icon that is part of the "Schedule a call" button.
You can use the secure messaging service on Clarity to work out the details of your call request, fill in an expert before your call to save time during the call, or just convey any correspondence you feel necessary.
NOTE: In order to add separate lines in a message, simply click Shift+Enter or Ctrl+Enter on Windows/Linux.