Contact is customer and supplier

Contact is client and supplier

If you have a contact in your addressbook that is both a supplier AND client, you need to add this in the settings of the specific contact, before it is visible. 

How do I do this? 
Go to your address book and search for the specific contact. On the second tab make sure both 'is client' and 'is supplier' are selected (marked green).

Don't forget tio click save!