Please check with your business that they want to use the same Revenue Account for both transaction and credit memo.
If yes, AR: Use Invoice Accounting for Credit Memos is set to Yes other set it to NO.
Here is detail related to above profile.
"Note: Receivables does not require you to enter a Revenue Account
for Credit Memo transaction types if the profile option
AR: Use Invoice Accounting for Credit Memos is set to Yes.
Otherwise, you must enter a Revenue Account."
"AR: Use Invoice Accounting for Credit Memos:
This profile option determines whether to assign your credit memo
to the same accounts that are assigned to the invoice you are
crediting.
The value for this option can be set by the system administrator
at the site, application, responsibility, and user levels, but
cannot be updated by the user."
