To Add Additional users/contacts in the Client Portal, you need to -
1. Log in to your Client area.
2. Go to Manage Contacts.
3. Click on "Add New Contact"
4. Fill up the asked details on the page.
5. Scroll down to the same page and grant the new client the privileges you want for your account.
6. Once done click on "Submit". New contacts will be added to your account.