If there is a need to mark a customer as InterCompany (IC) this is done on the client card in the tab Reminders/Payments with a check box. It's also possible to set the IC-code.

Press Save when done.

Clients marked with IC can be found in the statistic module. Checkmark the box in the customer tab.

The Intercompany account can be connected to a specific Payment method.

The Intercompany code also has a field in the accounting section.