My understanding is where an entity is both a supplier and customer you need to enter the entity into Manager twice
- As a customer in the customer tab
- As a supplier in the supplier tab
Purchase and sales Invoices with that entity can then be created.
Then when a financial transaction occurs the payment or receipt can then have line items to both accounts receivable and accounts payable. The full transaction can be documented by by printing all of
- Payment / Receipt
- Sales invoice
- Purchase invoice
The disadvantage of Managers current implementation of contacts is it cannot generate a statement for that entity (only separate supplier and customer statements for each part of the business interaction). A possible solution is to combine the supplier and customer databases into a contacts database as described here Copy Customer to Supplier and vice versa - #2 by Patch Manager could then product a statement for that entity (in both of their roles) which you could then send to them, requesting payment of the net balance. Which I think was the function of the problematic invoice above.
The problem you have addressed is part of a more general opportunity for Manager: How to better handle invoiced Barter transactions and Recipient-created tax invoices (RCTI) in Manager.
With Manager “cash” sales this can be approximated in one transaction by selecting Payer/Payee type “Other”.