Problem: I have Payable balance and Advance Paid to the same company but I cannot allocate these prepayments due to some reason (Back dated Invoices, Wrong Orders specified), how can I adjust such balances?
Solution:
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Use Mutual Settlement document with Supplier Debt Assignment as shown.
1) . Company Martin Torth has the payable invoice dated and Advance Payment dated Bothe Bothe of them are linked to different Purchase Orders: 
2) . In order to adjust these two entries create Mutual Settlement with Transaction Type Supplier Debt Assignment. In both Supplier and Supplier Recipient fields put the concerned company:
3) . In Accounts Payable Tab Select Invoice Received using Pick Option: 
4) . In Payee Attributes Tab Select the Contract, Payment Document and Purchase Order that is linked to the Payment Document, Amount of Settlement should be equal to the amount in Accounts Payable Tab : . It is Important to fill all fields, otherwise the document will not be posted:
5) . Post the document. The Mutual Settlement will create following transaction:
And Supplier's Account will be adjusted: 
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