Not possible to update busn. vols. for reb. arr. (cond. record settled)

What causes this issue?

Although settlement accounting has not yet been carried out for rebate
arrangement &V1&, the condition record for the document conditions has
been assigned the status "Settled".

System Response

Since no further settlement accounting is planned for the condition
record, no supplier business volume data can be updated.

How to fix this error?

This situation should not normally arise (program error). You should
therefore contact your system administrator.
You can also proceed as follows:
Check whether the supplier business volume data is to be taken into
account.
If so, cancel the settlement document(s) relating to the condition
record. This will cause the status of the condition record to be reset
to "Active".
Update the cumulative business volume data retrospectively using one of
the functions provided for the purpose.
Using the relevant functions/reports, check whether there are any
further open transactions (purchase orders, goods receipts, supplier
invoices).

Error message extract from SAP system. Copyright SAP SE.