Clients are a feature of Premium Independent and Premium Team Projects. Only one Client is allowed per Project. Only Admins of Premium Independent and Premium Team Projects can invite Clients.
To invite a Client, go to the Admin tab within your Project:
Here you will see the option to add a Client:
Simply type in the Client's email and click add:
An email with a link to join your project will be sent to your Client.
To see all the benefits of upgrading your Independent Project or Team to Premium, click here.