I'm trying to create a separate credit memo and apply credit memo to an existing invoice. Does this only work for open invoices? If so, is there a way to reopen the invoice before I apply the credit memo?

Create the credit memo Then create a customer payment and apply the payment to both the invoice and credit memo The customer payment will be net $0 and “disappear” and the CM will apply to invoice

The only problem is that I'm moving partial refund from another system to Netsuite Credit Memo. When I did research, the only way to transform it into partial credit memo is to scale down the amount by ratio. However, it is causing mismatch due to rounding issue.