RE: National Accounts for Customers (Or Vendors)
Hello Lisa,
There isn't National (Parent) Customers in Dynamics 365 for Finance and Operations, Business Edition. Please consider entering a product suggestion to have this functionality added. Suggestions can be added here:
https://ideas.dynamics.com/ideas/dynamics-financials
However, there is a way to set up customers so that when you Invoice one customer another customer is the one responsible for paying, which may not be all the functionality that you are looking for, but I wanted to let you know about this.
This functionality can be accomplished by creating multiple customers and then assigning the paying customer to the other Customer's Card under the Invoicing tab. For example, I create Customer A and Customer B. Customer A is who I sell products to, but Customer B pays for them. I set these Customers both up in the system and then on Customer A's card I select Customer B as the Customer under the Invoicing area, see screenshot below:

When an Invoice is created for Customer A, it is sent to Customer B's ledger and is outstanding for Customer B. Customer A has nothing outstanding.
Thank you,
Jennifer Reinhardt
Please see our Dynamics 365 Financials Support Team Blog for helpful information:
https://blogs.msdn.microsoft.com/dyn365finsupport/