Did you create the customer in your database first? When we have a new customer we always create the customer first.
In Web Access, you can go to the main menu and create customer. Then go back out to the main menu and create an invoice or draft as normal.
From your main computer, you can either go to customer area and add a new one, or in your create invoice screen, there is a little icon that looks like 3 people next to the Customer Name field. Click on that. This will bring you to the customer list. Click on Add at the top. Once you've added the customer, click on Select at the top. That will automatically add the new customer to the invoice you are creating.
Hope this helps!
Teri