Debit and Credit memo generation from PPM Contracts

We are using Amount based invoicing method to generate sales invoices from PPM Contracts. Our requirement is to generate a Receivable debit memo and credit memo from the PPM contract. Could you please suggest ways and processing of those invoices and credit/debit memos?

By creating an event with a negative amount, it is generating a standard sales invoice with a negative value.

But if we update the amount on the event in that case it's generating, a credit memo for the original transaction and a new invoice with the updated amount.