How to transfer credit between customers?

How to transfer credit between customers?

Hi All,

We have a slightly odd situation. It happens that we have two separate customers that are related to each other personally. One customer has an amount of credit, and would like to use that credit to pay the *other* customers invoice.

How would we go about achieving this in Zoho Books?

The way that we were thinking was to "refund" the customer credit to cash and use that cash to pay the Invoice of the other customer. However we do not know how to refund the customer credit as there is no credit note. 

Any ideas?