You need to add a customer with the customer # the same as the National account code.  In other words, the National account 'parent' must be a customer too.

What is the relationship here? Is it "one to one" or can it be "one to many", where the latter is one main account with several sub accounts?

One national = many customer

Then how do you create one national # and many customers with the same national account code? I don't really understand how this should go. Please clarify further perhaps with an example  of "One National =  Many Customers".

Read the documentation, and look at BARMART in Sample Company.

Ok will do that. I just need to know whether there is a separate documentation for National Accounts or is it just a section under Chapter 2 of A/R User Guide?

Open the A/R National Screen and press F1.  That's all there is.

Herewith the steps that I have followed in trying to get the National Accounts to work. Note that the Customers already had transactions before National Accounts was purchased and activated.

1. Created a National Account in A/R Customers > National Accounts - i.e. NMDS01.

2. Created a customer with a customer # similar to National Account in A/R Customers > Customers - i.e. NMDS01.

3. Linked the existing customers to a National Account by modifying the customers in A/R Customers > Customers

However, I still get the error "Customer is not a national account branch office.".

What step could I possibly have missed?