There is a transaction in the purchase invoice and the sales invoice

There is a transaction in the purchase invoice and the sales invoice. (A supplier and a customer) may have a sales invoice, a purchase invoice, and a financial payment account other than the purchase invoice and the sales invoice. The sales invoice manager system is an account and the purchase invoice is an account. We need to merge them together, because the customer It has a sales invoice and a purchase invoice. We need to explain if there is a method or add it in the next version

See this guide https://www2.manager.io/guides/9655