Someone was frenetically searching for an API to create a credit memo in AR. Certainly there are APIs available to create a credit memo, but the issue is that all of them allow creating a credit memo only against an existing invoice and not on account credit. If you have read the Receivables reference guide it clearly tells you to that the AR_CREDIT_MEMO_API_PUB.create_request cannot be used to create on-account credit memos.
But you can always use AR Interface tables to create on-account credit memo. While there is no recommendation on which one is better, personally my choice is always based on the volume. If it is batch processing, I always prefer using ra_interface_lines_all, ra_interface_sales_credits_all and ra_interface_distributions_all. If it is unit transaction, I prefer API approach as the I can reduce unnecessary coding required to insert and then call the auto-invoice interface and then monitor it whether it is completed or not.
The API in focus here is ar_transaction_pub.create_transaction. Using this you can create all types of transactions that can be created in AR.
Bad news is this can only be used till 11.5.10. In R12, this API has been obsoleted. From R12, the only way you can create on-account credit memos is using Auto Invoice Interface.