Using the accounting distributions on a vendor invoice line does not allow the user to enter add a line with an amount with a sign different from the source document line.
It is sometimes required to add a credit line to a vendor invoice if the vendor has something withdrawn and the ledger account must be a different account than the original account.
Total invoice: 50,00
Split in accounting distribution by the invoice approver:
1 line: 100,00
2 line: -50,00
This is not possible and the message is:
The sign of the amount and quantity on the accounting distributions must match the sign on the source document line.
(The invoice approver cannot add new vendor invoices lines as the invoice is active in a workflow)