In order to invite a client into Client Discovery, you first have to add the client contact within the Clients Contacts module.
The quickest way to add multiple clients is to bulk add them through an upload. To do so you can download the client_contact_upload.xlsx from this webpage.
Otherwise, you can do so one at a time through the New Contact button.
To create a contact fill in Name, Company, and Email. Once you are finished click Create Contact
If you are in a hurry or if you find it convenient to add the Client on the fly. [Link:] Find out how to do that here.