In Adagio Payables, the 'Open Payables' report will label an invoice with a 'C' for 'Completely settled by post-dated transactions' if there is one or more matching transactions applied to the invoice - with a date later than the report date - that sets the current amount of the invoice to zero.

And when you indicate that these invoices will not clear, do you mean to move these completed invoices from Current to History in Payables?

Firstly, do an inquiry to the vendor transaction and look at the applied details (ie payment, credit note, etc). Are there any and what is the transaction date? If you printed the Open Payables report with a date later than these applied detail dates, how do the invoices look on the report?

When you run period date to purge completed transactions to history, all transactions must be earlier than the purge date. If the payment date is later than the purge date, then not only will the payment not be purged, but neither will the invoices that it paid. This likely is why Adagio Payables is not clearing these invoices - if there are post-dated payments or credit notes on file, applied to these invoices.