How to perform Document Sequence for Payment Request ?

The document sequence for the "payment request" should be created under invoice level or the payment level for performing AR credit memo refund? Is there any difference under Invoice & Payment level?

I have one AR transaction which was not able to perform CM refund due to Error :The refund wasn't processed because the Payables invoice wasn't created for the following reasons: Invalid assignment. (AR-856622). So setup document sequence assignment under Payment level in "Manage Payables Document Sequence" & tested with success.

Now User is asking : the document sequence for the payment request should be created at the invoice level rather than the payment level. Because another consultant created the above setup under Invoice level & it was also succeeded.