Invoice Settings controls how open invoices for Bill to Account orders are handled.
To open it, click Settings in the top navigation bar, then Invoice Settings under Payments. Click Save changes when you're done.
Make Open Bills Required
Check Make open bills required to require accounts to pay their open invoices.
Invoices are only for Bill to Account charges, such as snack bar purchases charged to an account. See How Billing Works in Member Splash: Payments vs. Invoices.
To change how invoices look, use Settings → Invoice Branding.