The Metering system has made an error according to the usage quantity: the customer invoice...

Create a Credit Memo for Contract account with transaction 0010/0010.

Create with Billing Request for Correction a new billable item with quantity –5.

Correct the billed item in billable item monitor quantity from 10 to 5.

Create a Billing and Invoicing Reversal Document and rerun Billing and Invoicing.