Consider the following scenario:

A purchase order for a vendor is prepaid: a prepayment invoice is posted and paid to the vendor.

Then, the items are received but less then ordered. And the remaining quantity will not be received. 

Instead, the vendor says to keep the amount which was now over-paid as ‘credit’ to apply to future invoices.

There is no easy way to handle this in BC, other then posting a prepayment credit memo and updating the purchase order.

Really there should be an easier way for this.

And in general, the prepayment functionality in BC is not very user-friendly or even functional.

See also: https://experience.dynamics.com/ideas/idea/?ideaid=769d3ce7-d4cd-eb11-ba5e-0003ff45ac2b