Clients can have multiple contacts, which is great for tracking parents, siblings, entire families, teachers, employers etc. Contacts can have appointments and invoices too as well as receive appointment reminders for the client's appointments.
You are also able to add an existing client as a contact. For example if two existing clients are partners or a parent and child you are able to resemble this relationship by adding one of the clients as a contact for the other client.
To Add an existing Client as a Contact:
1. Go into the clients record (Clients> Search)
2. Go into the Contacts section
3. Click "Add a Contact"
4. Use the search field to search for the clients name
5. Edit any details and click 'Save'
You can search for contacts in the clients search by changing the 'Other Business Contacts' filter from 'Customer' to 'Customer Contact'.