how does the customer posting groups determine the receivables account in Business Central?
The customer posting group determines the receivables account.
This is what happens in the video
You define customer posting groups and the customer posting group is assigned to the customers in the system.
When you create new documents or journals directly, this customer posting group will be transferred to those documents and those journals, which means when you do posting, the customer posting group will have set up accounts that determines, where to post your receivables but also your discount accounts, in your income statement.
The receivable is the balance account and your service charge account.